Split (1)

train · 39.1k rows

task stringlengths 0 154k	__index_level_0__ int64 0 39.2k
--- Day 23: Coprocessor Conflagration --- You decide to head directly to the CPU and fix the printer from there. As you get close, you find an experimental coprocessor doing so much work that the local programs are afraid it will halt and catch fire. This would cause serious issues for the rest of the computer, so you head in and see what you can do. The code it's running seems to be a variant of the kind you saw recently on that tablet. The general functionality seems very similar, but some of the instructions are different: set X Y sets register X to the value of Y. sub X Y decreases register X by the value of Y. mul X Y sets register X to the result of multiplying the value contained in register X by the value of Y. jnz X Y jumps with an offset of the value of Y, but only if the value of X is not zero. (An offset of 2 skips the next instruction, an offset of -1 jumps to the previous instruction, and so on.) Only the instructions listed above are used. The eight registers here, named a through h, all start at 0. The coprocessor is currently set to some kind of debug mode, which allows for testing, but prevents it from doing any meaningful work. If you run the program (your puzzle input), how many times is the mul instruction invoked? Your puzzle answer was 3025. --- Part Two --- Now, it's time to fix the problem. The debug mode switch is wired directly to register a. You flip the switch, which makes register a now start at 1 when the program is executed. Immediately, the coprocessor begins to overheat. Whoever wrote this program obviously didn't choose a very efficient implementation. You'll need to optimize the program if it has any hope of completing before Santa needs that printer working. The coprocessor's ultimate goal is to determine the final value left in register h once the program completes. Technically, if it had that... it wouldn't even need to run the program. After setting register a to 1, if the program were to run to completion, what value would be left in register h?	0
--- Day 10: The Stars Align --- It's no use; your navigation system simply isn't capable of providing walking directions in the arctic circle, and certainly not in 1018. The Elves suggest an alternative. In times like these, North Pole rescue operations will arrange points of light in the sky to guide missing Elves back to base. Unfortunately, the message is easy to miss: the points move slowly enough that it takes hours to align them, but have so much momentum that they only stay aligned for a second. If you blink at the wrong time, it might be hours before another message appears. You can see these points of light floating in the distance, and record their position in the sky and their velocity, the relative change in position per second (your puzzle input). The coordinates are all given from your perspective; given enough time, those positions and velocities will move the points into a cohesive message! Rather than wait, you decide to fast-forward the process and calculate what the points will eventually spell. For example, suppose you note the following points: position=< 9, 1> velocity=< 0, 2> position=< 7, 0> velocity=<-1, 0> position=< 3, -2> velocity=<-1, 1> position=< 6, 10> velocity=<-2, -1> position=< 2, -4> velocity=< 2, 2> position=<-6, 10> velocity=< 2, -2> position=< 1, 8> velocity=< 1, -1> position=< 1, 7> velocity=< 1, 0> position=<-3, 11> velocity=< 1, -2> position=< 7, 6> velocity=<-1, -1> position=<-2, 3> velocity=< 1, 0> position=<-4, 3> velocity=< 2, 0> position=<10, -3> velocity=<-1, 1> position=< 5, 11> velocity=< 1, -2> position=< 4, 7> velocity=< 0, -1> position=< 8, -2> velocity=< 0, 1> position=<15, 0> velocity=<-2, 0> position=< 1, 6> velocity=< 1, 0> position=< 8, 9> velocity=< 0, -1> position=< 3, 3> velocity=<-1, 1> position=< 0, 5> velocity=< 0, -1> position=<-2, 2> velocity=< 2, 0> position=< 5, -2> velocity=< 1, 2> position=< 1, 4> velocity=< 2, 1> position=<-2, 7> velocity=< 2, -2> position=< 3, 6> velocity=<-1, -1> position=< 5, 0> velocity=< 1, 0> position=<-6, 0> velocity=< 2, 0> position=< 5, 9> velocity=< 1, -2> position=<14, 7> velocity=<-2, 0> position=<-3, 6> velocity=< 2, -1> Each line represents one point. Positions are given as <X, Y> pairs: X represents how far left (negative) or right (positive) the point appears, while Y represents how far up (negative) or down (positive) the point appears. At 0 seconds, each point has the position given. Each second, each point's velocity is added to its position. So, a point with velocity <1, -2> is moving to the right, but is moving upward twice as quickly. If this point's initial position were <3, 9>, after 3 seconds, its position would become <6, 3>. Over time, the points listed above would move like this: Initially: ........#............. ................#..... .........#.#..#....... ...................... #..........#.#.......# ...............#...... ....#................. ..#.#....#............ .......#.............. ......#............... ...#...#.#...#........ ....#..#..#.........#. .......#.............. ...........#..#....... #...........#......... ...#.......#.......... After 1 second: ...................... ...................... ..........#....#...... ........#.....#....... ..#.........#......#.. ...................... ......#............... ....##.........#...... ......#.#............. .....##.##..#......... ........#.#........... ........#...#.....#... ..#...........#....... ....#.....#.#......... ...................... ...................... After 2 seconds: ...................... ...................... ...................... ..............#....... ....#..#...####..#.... ...................... ........#....#........ ......#.#............. .......#...#.......... .......#..#..#.#...... ....#....#.#.......... .....#...#...##.#..... ........#............. ...................... ...................... ...................... After 3 seconds: ...................... ...................... ...................... ...................... ......#...#..###...... ......#...#...#....... ......#...#...#....... ......#####...#....... ......#...#...#....... ......#...#...#....... ......#...#...#....... ......#...#..###...... ...................... ...................... ...................... ...................... After 4 seconds: ...................... ...................... ...................... ............#......... ........##...#.#...... ......#.....#..#...... .....#..##.##.#....... .......##.#....#...... ...........#....#..... ..............#....... ....#......#...#...... .....#.....##......... ...............#...... ...............#...... ...................... ...................... After 3 seconds, the message appeared briefly: HI. Of course, your message will be much longer and will take many more seconds to appear. What message will eventually appear in the sky?	1
--- Day 16: Reindeer Maze --- It's time again for the Reindeer Olympics! This year, the big event is the Reindeer Maze, where the Reindeer compete for the lowest score. You and The Historians arrive to search for the Chief right as the event is about to start. It wouldn't hurt to watch a little, right? The Reindeer start on the Start Tile (marked S) facing East and need to reach the End Tile (marked E). They can move forward one tile at a time (increasing their score by 1 point), but never into a wall (#). They can also rotate clockwise or counterclockwise 90 degrees at a time (increasing their score by 1000 points). To figure out the best place to sit, you start by grabbing a map (your puzzle input) from a nearby kiosk. For example: ############### #.......#....E# #.#.###.#.###.# #.....#.#...#.# #.###.#####.#.# #.#.#.......#.# #.#.#####.###.# #...........#.# ###.#.#####.#.# #...#.....#.#.# #.#.#.###.#.#.# #.....#...#.#.# #.###.#.#.#.#.# #S..#.....#...# ############### There are many paths through this maze, but taking any of the best paths would incur a score of only 7036. This can be achieved by taking a total of 36 steps forward and turning 90 degrees a total of 7 times: ############### #.......#....E# #.#.###.#.###^# #.....#.#...#^# #.###.#####.#^# #.#.#.......#^# #.#.#####.###^# #..>>>>>>>>v#^# ###^#.#####v#^# #>>^#.....#v#^# #^#.#.###.#v#^# #^....#...#v#^# #^###.#.#.#v#^# #S..#.....#>>^# ############### Here's a second example: ################# #...#...#...#..E# #.#.#.#.#.#.#.#.# #.#.#.#...#...#.# #.#.#.#.###.#.#.# #...#.#.#.....#.# #.#.#.#.#.#####.# #.#...#.#.#.....# #.#.#####.#.###.# #.#.#.......#...# #.#.###.#####.### #.#.#...#.....#.# #.#.#.#####.###.# #.#.#.........#.# #.#.#.#########.# #S#.............# ################# In this maze, the best paths cost 11048 points; following one such path would look like this: ################# #...#...#...#..E# #.#.#.#.#.#.#.#^# #.#.#.#...#...#^# #.#.#.#.###.#.#^# #>>v#.#.#.....#^# #^#v#.#.#.#####^# #^#v..#.#.#>>>>^# #^#v#####.#^###.# #^#v#..>>>>^#...# #^#v###^#####.### #^#v#>>^#.....#.# #^#v#^#####.###.# #^#v#^........#.# #^#v#^#########.# #S#>>^..........# ################# Note that the path shown above includes one 90 degree turn as the very first move, rotating the Reindeer from facing East to facing North. Analyze your map carefully. What is the lowest score a Reindeer could possibly get? Your puzzle answer was 95444. The first half of this puzzle is complete! It provides one gold star: * --- Part Two --- Now that you know what the best paths look like, you can figure out the best spot to sit. Every non-wall tile (S, ., or E) is equipped with places to sit along the edges of the tile. While determining which of these tiles would be the best spot to sit depends on a whole bunch of factors (how comfortable the seats are, how far away the bathrooms are, whether there's a pillar blocking your view, etc.), the most important factor is whether the tile is on one of the best paths through the maze. If you sit somewhere else, you'd miss all the action! So, you'll need to determine which tiles are part of any best path through the maze, including the S and E tiles. In the first example, there are 45 tiles (marked O) that are part of at least one of the various best paths through the maze: ############### #.......#....O# #.#.###.#.###O# #.....#.#...#O# #.###.#####.#O# #.#.#.......#O# #.#.#####.###O# #..OOOOOOOOO#O# ###O#O#####O#O# #OOO#O....#O#O# #O#O#O###.#O#O# #OOOOO#...#O#O# #O###.#.#.#O#O# #O..#.....#OOO# ############### In the second example, there are 64 tiles that are part of at least one of the best paths: ################# #...#...#...#..O# #.#.#.#.#.#.#.#O# #.#.#.#...#...#O# #.#.#.#.###.#.#O# #OOO#.#.#.....#O# #O#O#.#.#.#####O# #O#O..#.#.#OOOOO# #O#O#####.#O###O# #O#O#..OOOOO#OOO# #O#O###O#####O### #O#O#OOO#..OOO#.# #O#O#O#####O###.# #O#O#OOOOOOO..#.# #O#O#O#########.# #O#OOO..........# ################# Analyze your map further. How many tiles are part of at least one of the best paths through the maze?	2
--- Day 16: Ticket Translation --- As you're walking to yet another connecting flight, you realize that one of the legs of your re-routed trip coming up is on a high-speed train. However, the train ticket you were given is in a language you don't understand. You should probably figure out what it says before you get to the train station after the next flight. Unfortunately, you can't actually read the words on the ticket. You can, however, read the numbers, and so you figure out the fields these tickets must have and the valid ranges for values in those fields. You collect the rules for ticket fields, the numbers on your ticket, and the numbers on other nearby tickets for the same train service (via the airport security cameras) together into a single document you can reference (your puzzle input). The rules for ticket fields specify a list of fields that exist somewhere on the ticket and the valid ranges of values for each field. For example, a rule like class: 1-3 or 5-7 means that one of the fields in every ticket is named class and can be any value in the ranges 1-3 or 5-7 (inclusive, such that 3 and 5 are both valid in this field, but 4 is not). Each ticket is represented by a single line of comma-separated values. The values are the numbers on the ticket in the order they appear; every ticket has the same format. For example, consider this ticket: .--------------------------------------------------------. \| ????: 101 ?????: 102 ??????????: 103 ???: 104 \| \| \| \| ??: 301 ??: 302 ???????: 303 ??????? \| \| ??: 401 ??: 402 ???? ????: 403 ????????? \| '--------------------------------------------------------' Here, ? represents text in a language you don't understand. This ticket might be represented as 101,102,103,104,301,302,303,401,402,403; of course, the actual train tickets you're looking at are much more complicated. In any case, you've extracted just the numbers in such a way that the first number is always the same specific field, the second number is always a different specific field, and so on - you just don't know what each position actually means! Start by determining which tickets are completely invalid; these are tickets that contain values which aren't valid for any field. Ignore your ticket for now. For example, suppose you have the following notes: class: 1-3 or 5-7 row: 6-11 or 33-44 seat: 13-40 or 45-50 your ticket: 7,1,14 nearby tickets: 7,3,47 40,4,50 55,2,20 38,6,12 It doesn't matter which position corresponds to which field; you can identify invalid nearby tickets by considering only whether tickets contain values that are not valid for any field. In this example, the values on the first nearby ticket are all valid for at least one field. This is not true of the other three nearby tickets: the values 4, 55, and 12 are are not valid for any field. Adding together all of the invalid values produces your ticket scanning error rate: 4 + 55 + 12 = 71. Consider the validity of the nearby tickets you scanned. What is your ticket scanning error rate?	3
--- Day 18: Like a Rogue --- As you enter this room, you hear a loud click! Some of the tiles in the floor here seem to be pressure plates for traps, and the trap you just triggered has run out of... whatever it tried to do to you. You doubt you'll be so lucky next time. Upon closer examination, the traps and safe tiles in this room seem to follow a pattern. The tiles are arranged into rows that are all the same width; you take note of the safe tiles (.) and traps (^) in the first row (your puzzle input). The type of tile (trapped or safe) in each row is based on the types of the tiles in the same position, and to either side of that position, in the previous row. (If either side is off either end of the row, it counts as "safe" because there isn't a trap embedded in the wall.) For example, suppose you know the first row (with tiles marked by letters) and want to determine the next row (with tiles marked by numbers): ABCDE 12345 The type of tile 2 is based on the types of tiles A, B, and C; the type of tile 5 is based on tiles D, E, and an imaginary "safe" tile. Let's call these three tiles from the previous row the left, center, and right tiles, respectively. Then, a new tile is a trap only in one of the following situations: Its left and center tiles are traps, but its right tile is not. Its center and right tiles are traps, but its left tile is not. Only its left tile is a trap. Only its right tile is a trap. In any other situation, the new tile is safe. Then, starting with the row ..^^., you can determine the next row by applying those rules to each new tile: The leftmost character on the next row considers the left (nonexistent, so we assume "safe"), center (the first ., which means "safe"), and right (the second ., also "safe") tiles on the previous row. Because all of the trap rules require a trap in at least one of the previous three tiles, the first tile on this new row is also safe, .. The second character on the next row considers its left (.), center (.), and right (^) tiles from the previous row. This matches the fourth rule: only the right tile is a trap. Therefore, the next tile in this new row is a trap, ^. The third character considers .^^, which matches the second trap rule: its center and right tiles are traps, but its left tile is not. Therefore, this tile is also a trap, ^. The last two characters in this new row match the first and third rules, respectively, and so they are both also traps, ^. After these steps, we now know the next row of tiles in the room: .^^^^. Then, we continue on to the next row, using the same rules, and get ^^..^. After determining two new rows, our map looks like this: ..^^. .^^^^ ^^..^ Here's a larger example with ten tiles per row and ten rows: .^^.^.^^^^ ^^^...^..^ ^.^^.^.^^. ..^^...^^^ .^^^^.^^.^ ^^..^.^^.. ^^^^..^^^. ^..^^^^.^^ .^^^..^.^^ ^^.^^^..^^ In ten rows, this larger example has 38 safe tiles. Starting with the map in your puzzle input, in a total of 40 rows (including the starting row), how many safe tiles are there?	4
--- Day 20: Trench Map --- With the scanners fully deployed, you turn their attention to mapping the floor of the ocean trench. When you get back the image from the scanners, it seems to just be random noise. Perhaps you can combine an image enhancement algorithm and the input image (your puzzle input) to clean it up a little. For example: ..#.#..#####.#.#.#.###.##.....###.##.#..###.####..#####..#....#..#..##..## #..######.###...####..#..#####..##..#.#####...##.#.#..#.##..#.#......#.### .######.###.####...#.##.##..#..#..#####.....#.#....###..#.##......#.....#. .#..#..##..#...##.######.####.####.#.#...#.......#..#.#.#...####.##.#..... .#..#...##.#.##..#...##.#.##..###.#......#.#.......#.#.#.####.###.##...#.. ...####.#..#..#.##.#....##..#.####....##...##..#...#......#.#.......#..... ..##..####..#...#.#.#...##..#.#..###..#####........#..####......#..# #..#. #.... ##..# ..#.. ..### The first section is the image enhancement algorithm. It is normally given on a single line, but it has been wrapped to multiple lines in this example for legibility. The second section is the input image, a two-dimensional grid of light pixels (#) and dark pixels (.). The image enhancement algorithm describes how to enhance an image by simultaneously converting all pixels in the input image into an output image. Each pixel of the output image is determined by looking at a 3x3 square of pixels centered on the corresponding input image pixel. So, to determine the value of the pixel at (5,10) in the output image, nine pixels from the input image need to be considered: (4,9), (4,10), (4,11), (5,9), (5,10), (5,11), (6,9), (6,10), and (6,11). These nine input pixels are combined into a single binary number that is used as an index in the image enhancement algorithm string. For example, to determine the output pixel that corresponds to the very middle pixel of the input image, the nine pixels marked by [...] would need to be considered: # . . # . #[. . .]. #[# . .]# .[. # .]. . . # # # Starting from the top-left and reading across each row, these pixels are ..., then #.., then .#.; combining these forms ...#...#.. By turning dark pixels (.) into 0 and light pixels (#) into 1, the binary number 000100010 can be formed, which is 34 in decimal. The image enhancement algorithm string is exactly 512 characters long, enough to match every possible 9-bit binary number. The first few characters of the string (numbered starting from zero) are as follows: 0 10 20 30 34 40 50 60 70 \| \| \| \| \| \| \| \| \| ..#.#..#####.#.#.#.###.##.....###.##.#..###.####..#####..#....#..#..##..## In the middle of this first group of characters, the character at index 34 can be found: #. So, the output pixel in the center of the output image should be #, a light pixel. This process can then be repeated to calculate every pixel of the output image. Through advances in imaging technology, the images being operated on here are infinite in size. Every pixel of the infinite output image needs to be calculated exactly based on the relevant pixels of the input image. The small input image you have is only a small region of the actual infinite input image; the rest of the input image consists of dark pixels (.). For the purposes of the example, to save on space, only a portion of the infinite-sized input and output images will be shown. The starting input image, therefore, looks something like this, with more dark pixels (.) extending forever in every direction not shown here: ............... ............... ............... ............... ............... .....#..#...... .....#......... .....##..#..... .......#....... .......###..... ............... ............... ............... ............... ............... By applying the image enhancement algorithm to every pixel simultaneously, the following output image can be obtained: ............... ............... ............... ............... .....##.##..... ....#..#.#..... ....##.#..#.... ....####..#.... .....#..##..... ......##..#.... .......#.#..... ............... ............... ............... ............... Through further advances in imaging technology, the above output image can also be used as an input image! This allows it to be enhanced a second time: ............... ............... ............... ..........#.... ....#..#.#..... ...#.#...###... ...#...##.#.... ...#.....#.#... ....#.#####.... .....#.#####... ......##.##.... .......###..... ............... ............... ............... Truly incredible - now the small details are really starting to come through. After enhancing the original input image twice, 35 pixels are lit. Start with the original input image and apply the image enhancement algorithm twice, being careful to account for the infinite size of the images. How many pixels are lit in the resulting image?	5
--- Day 12: Hill Climbing Algorithm --- You try contacting the Elves using your handheld device, but the river you're following must be too low to get a decent signal. You ask the device for a heightmap of the surrounding area (your puzzle input). The heightmap shows the local area from above broken into a grid; the elevation of each square of the grid is given by a single lowercase letter, where a is the lowest elevation, b is the next-lowest, and so on up to the highest elevation, z. Also included on the heightmap are marks for your current position (S) and the location that should get the best signal (E). Your current position (S) has elevation a, and the location that should get the best signal (E) has elevation z. You'd like to reach E, but to save energy, you should do it in as few steps as possible. During each step, you can move exactly one square up, down, left, or right. To avoid needing to get out your climbing gear, the elevation of the destination square can be at most one higher than the elevation of your current square; that is, if your current elevation is m, you could step to elevation n, but not to elevation o. (This also means that the elevation of the destination square can be much lower than the elevation of your current square.) For example: Sabqponm abcryxxl accszExk acctuvwj abdefghi Here, you start in the top-left corner; your goal is near the middle. You could start by moving down or right, but eventually you'll need to head toward the e at the bottom. From there, you can spiral around to the goal: v..v<<<< >v.vv<<^ .>vv>E^^ ..v>>>^^ ..>>>>>^ In the above diagram, the symbols indicate whether the path exits each square moving up (^), down (v), left (<), or right (>). The location that should get the best signal is still E, and . marks unvisited squares. This path reaches the goal in 31 steps, the fewest possible. What is the fewest steps required to move from your current position to the location that should get the best signal?	6
--- Day 19: Medicine for Rudolph --- Rudolph the Red-Nosed Reindeer is sick! His nose isn't shining very brightly, and he needs medicine. Red-Nosed Reindeer biology isn't similar to regular reindeer biology; Rudolph is going to need custom-made medicine. Unfortunately, Red-Nosed Reindeer chemistry isn't similar to regular reindeer chemistry, either. The North Pole is equipped with a Red-Nosed Reindeer nuclear fusion/fission plant, capable of constructing any Red-Nosed Reindeer molecule you need. It works by starting with some input molecule and then doing a series of replacements, one per step, until it has the right molecule. However, the machine has to be calibrated before it can be used. Calibration involves determining the number of molecules that can be generated in one step from a given starting point. For example, imagine a simpler machine that supports only the following replacements: H => HO H => OH O => HH Given the replacements above and starting with HOH, the following molecules could be generated: HOOH (via H => HO on the first H). HOHO (via H => HO on the second H). OHOH (via H => OH on the first H). HOOH (via H => OH on the second H). HHHH (via O => HH). So, in the example above, there are 4 distinct molecules (not five, because HOOH appears twice) after one replacement from HOH. Santa's favorite molecule, HOHOHO, can become 7 distinct molecules (over nine replacements: six from H, and three from O). The machine replaces without regard for the surrounding characters. For example, given the string H2O, the transition H => OO would result in OO2O. Your puzzle input describes all of the possible replacements and, at the bottom, the medicine molecule for which you need to calibrate the machine. How many distinct molecules can be created after all the different ways you can do one replacement on the medicine molecule? Your puzzle answer was 509. --- Part Two --- Now that the machine is calibrated, you're ready to begin molecule fabrication. Molecule fabrication always begins with just a single electron, e, and applying replacements one at a time, just like the ones during calibration. For example, suppose you have the following replacements: e => H e => O H => HO H => OH O => HH If you'd like to make HOH, you start with e, and then make the following replacements: e => O to get O O => HH to get HH H => OH (on the second H) to get HOH So, you could make HOH after 3 steps. Santa's favorite molecule, HOHOHO, can be made in 6 steps. How long will it take to make the medicine? Given the available replacements and the medicine molecule in your puzzle input, what is the fewest number of steps to go from e to the medicine molecule?	7
--- Day 15: Oxygen System --- Out here in deep space, many things can go wrong. Fortunately, many of those things have indicator lights. Unfortunately, one of those lights is lit: the oxygen system for part of the ship has failed! According to the readouts, the oxygen system must have failed days ago after a rupture in oxygen tank two; that section of the ship was automatically sealed once oxygen levels went dangerously low. A single remotely-operated repair droid is your only option for fixing the oxygen system. The Elves' care package included an Intcode program (your puzzle input) that you can use to remotely control the repair droid. By running that program, you can direct the repair droid to the oxygen system and fix the problem. The remote control program executes the following steps in a loop forever: Accept a movement command via an input instruction. Send the movement command to the repair droid. Wait for the repair droid to finish the movement operation. Report on the status of the repair droid via an output instruction. Only four movement commands are understood: north (1), south (2), west (3), and east (4). Any other command is invalid. The movements differ in direction, but not in distance: in a long enough east-west hallway, a series of commands like 4,4,4,4,3,3,3,3 would leave the repair droid back where it started. The repair droid can reply with any of the following status codes: 0: The repair droid hit a wall. Its position has not changed. 1: The repair droid has moved one step in the requested direction. 2: The repair droid has moved one step in the requested direction; its new position is the location of the oxygen system. You don't know anything about the area around the repair droid, but you can figure it out by watching the status codes. For example, we can draw the area using D for the droid, # for walls, . for locations the droid can traverse, and empty space for unexplored locations. Then, the initial state looks like this: D To make the droid go north, send it 1. If it replies with 0, you know that location is a wall and that the droid didn't move: # D To move east, send 4; a reply of 1 means the movement was successful: # .D Then, perhaps attempts to move north (1), south (2), and east (4) are all met with replies of 0: ## .D# # Now, you know the repair droid is in a dead end. Backtrack with 3 (which you already know will get a reply of 1 because you already know that location is open): ## D.# # Then, perhaps west (3) gets a reply of 0, south (2) gets a reply of 1, south again (2) gets a reply of 0, and then west (3) gets a reply of 2: ## #..# D.# # Now, because of the reply of 2, you know you've found the oxygen system! In this example, it was only 2 moves away from the repair droid's starting position. What is the fewest number of movement commands required to move the repair droid from its starting position to the location of the oxygen system?	8
--- Day 5: Supply Stacks --- The expedition can depart as soon as the final supplies have been unloaded from the ships. Supplies are stored in stacks of marked crates, but because the needed supplies are buried under many other crates, the crates need to be rearranged. The ship has a giant cargo crane capable of moving crates between stacks. To ensure none of the crates get crushed or fall over, the crane operator will rearrange them in a series of carefully-planned steps. After the crates are rearranged, the desired crates will be at the top of each stack. The Elves don't want to interrupt the crane operator during this delicate procedure, but they forgot to ask her which crate will end up where, and they want to be ready to unload them as soon as possible so they can embark. They do, however, have a drawing of the starting stacks of crates and the rearrangement procedure (your puzzle input). For example: [D] [N] [C] [Z] [M] [P] 1 2 3 move 1 from 2 to 1 move 3 from 1 to 3 move 2 from 2 to 1 move 1 from 1 to 2 In this example, there are three stacks of crates. Stack 1 contains two crates: crate Z is on the bottom, and crate N is on top. Stack 2 contains three crates; from bottom to top, they are crates M, C, and D. Finally, stack 3 contains a single crate, P. Then, the rearrangement procedure is given. In each step of the procedure, a quantity of crates is moved from one stack to a different stack. In the first step of the above rearrangement procedure, one crate is moved from stack 2 to stack 1, resulting in this configuration: [D] [N] [C] [Z] [M] [P] 1 2 3 In the second step, three crates are moved from stack 1 to stack 3. Crates are moved one at a time, so the first crate to be moved (D) ends up below the second and third crates: [Z] [N] [C] [D] [M] [P] 1 2 3 Then, both crates are moved from stack 2 to stack 1. Again, because crates are moved one at a time, crate C ends up below crate M: [Z] [N] [M] [D] [C] [P] 1 2 3 Finally, one crate is moved from stack 1 to stack 2: [Z] [N] [D] [C] [M] [P] 1 2 3 The Elves just need to know which crate will end up on top of each stack; in this example, the top crates are C in stack 1, M in stack 2, and Z in stack 3, so you should combine these together and give the Elves the message CMZ. After the rearrangement procedure completes, what crate ends up on top of each stack? Your puzzle answer was ZWHVFWQWW. --- Part Two --- As you watch the crane operator expertly rearrange the crates, you notice the process isn't following your prediction. Some mud was covering the writing on the side of the crane, and you quickly wipe it away. The crane isn't a CrateMover 9000 - it's a CrateMover 9001. The CrateMover 9001 is notable for many new and exciting features: air conditioning, leather seats, an extra cup holder, and the ability to pick up and move multiple crates at once. Again considering the example above, the crates begin in the same configuration: [D] [N] [C] [Z] [M] [P] 1 2 3 Moving a single crate from stack 2 to stack 1 behaves the same as before: [D] [N] [C] [Z] [M] [P] 1 2 3 However, the action of moving three crates from stack 1 to stack 3 means that those three moved crates stay in the same order, resulting in this new configuration: [D] [N] [C] [Z] [M] [P] 1 2 3 Next, as both crates are moved from stack 2 to stack 1, they retain their order as well: [D] [N] [C] [Z] [M] [P] 1 2 3 Finally, a single crate is still moved from stack 1 to stack 2, but now it's crate C that gets moved: [D] [N] [Z] [M] [C] [P] 1 2 3 In this example, the CrateMover 9001 has put the crates in a totally different order: MCD. Before the rearrangement process finishes, update your simulation so that the Elves know where they should stand to be ready to unload the final supplies. After the rearrangement procedure completes, what crate ends up on top of each stack?	9
--- Day 21: Keypad Conundrum --- As you teleport onto Santa's Reindeer-class starship, The Historians begin to panic: someone from their search party is missing. A quick life-form scan by the ship's computer reveals that when the missing Historian teleported, he arrived in another part of the ship. The door to that area is locked, but the computer can't open it; it can only be opened by physically typing the door codes (your puzzle input) on the numeric keypad on the door. The numeric keypad has four rows of buttons: 789, 456, 123, and finally an empty gap followed by 0A. Visually, they are arranged like this: +---+---+---+ \| 7 \| 8 \| 9 \| +---+---+---+ \| 4 \| 5 \| 6 \| +---+---+---+ \| 1 \| 2 \| 3 \| +---+---+---+ \| 0 \| A \| +---+---+ Unfortunately, the area outside the door is currently depressurized and nobody can go near the door. A robot needs to be sent instead. The robot has no problem navigating the ship and finding the numeric keypad, but it's not designed for button pushing: it can't be told to push a specific button directly. Instead, it has a robotic arm that can be controlled remotely via a directional keypad. The directional keypad has two rows of buttons: a gap / ^ (up) / A (activate) on the first row and < (left) / v (down) / > (right) on the second row. Visually, they are arranged like this: +---+---+ \| ^ \| A \| +---+---+---+ \| < \| v \| > \| +---+---+---+ When the robot arrives at the numeric keypad, its robotic arm is pointed at the A button in the bottom right corner. After that, this directional keypad remote control must be used to maneuver the robotic arm: the up / down / left / right buttons cause it to move its arm one button in that direction, and the A button causes the robot to briefly move forward, pressing the button being aimed at by the robotic arm. For example, to make the robot type 029A on the numeric keypad, one sequence of inputs on the directional keypad you could use is: < to move the arm from A (its initial position) to 0. A to push the 0 button. ^A to move the arm to the 2 button and push it. >^^A to move the arm to the 9 button and push it. vvvA to move the arm to the A button and push it. In total, there are three shortest possible sequences of button presses on this directional keypad that would cause the robot to type 029A: <A^A>^^AvvvA, <A^A^>^AvvvA, and <A^A^^>AvvvA. Unfortunately, the area containing this directional keypad remote control is currently experiencing high levels of radiation and nobody can go near it. A robot needs to be sent instead. When the robot arrives at the directional keypad, its robot arm is pointed at the A button in the upper right corner. After that, a second, different directional keypad remote control is used to control this robot (in the same way as the first robot, except that this one is typing on a directional keypad instead of a numeric keypad). There are multiple shortest possible sequences of directional keypad button presses that would cause this robot to tell the first robot to type 029A on the door. One such sequence is v<<A>>^A<A>AvA<^AA>A<vAAA>^A. Unfortunately, the area containing this second directional keypad remote control is currently -40 degrees! Another robot will need to be sent to type on that directional keypad, too. There are many shortest possible sequences of directional keypad button presses that would cause this robot to tell the second robot to tell the first robot to eventually type 029A on the door. One such sequence is <vA<AA>>^AvAA<^A>A<v<A>>^AvA^A<vA>^A<v<A>^A>AAvA^A<v<A>A>^AAAvA<^A>A. Unfortunately, the area containing this third directional keypad remote control is currently full of Historians, so no robots can find a clear path there. Instead, you will have to type this sequence yourself. Were you to choose this sequence of button presses, here are all of the buttons that would be pressed on your directional keypad, the two robots' directional keypads, and the numeric keypad: <vA<AA>>^AvAA<^A>A<v<A>>^AvA^A<vA>^A<v<A>^A>AAvA^A<v<A>A>^AAAvA<^A>A v<<A>>^A<A>AvA<^AA>A<vAAA>^A <A^A>^^AvvvA 029A In summary, there are the following keypads: One directional keypad that you are using. Two directional keypads that robots are using. One numeric keypad (on a door) that a robot is using. It is important to remember that these robots are not designed for button pushing. In particular, if a robot arm is ever aimed at a gap where no button is present on the keypad, even for an instant, the robot will panic unrecoverably. So, don't do that. All robots will initially aim at the keypad's A key, wherever it is. To unlock the door, five codes will need to be typed on its numeric keypad. For example: 029A 980A 179A 456A 379A For each of these, here is a shortest sequence of button presses you could type to cause the desired code to be typed on the numeric keypad: 029A: <vA<AA>>^AvAA<^A>A<v<A>>^AvA^A<vA>^A<v<A>^A>AAvA^A<v<A>A>^AAAvA<^A>A 980A: <v<A>>^AAAvA^A<vA<AA>>^AvAA<^A>A<v<A>A>^AAAvA<^A>A<vA>^A<A>A 179A: <v<A>>^A<vA<A>>^AAvAA<^A>A<v<A>>^AAvA^A<vA>^AA<A>A<v<A>A>^AAAvA<^A>A 456A: <v<A>>^AA<vA<A>>^AAvAA<^A>A<vA>^A<A>A<vA>^A<A>A<v<A>A>^AAvA<^A>A 379A: <v<A>>^AvA^A<vA<AA>>^AAvA<^A>AAvA^A<vA>^AA<A>A<v<A>A>^AAAvA<^A>A The Historians are getting nervous; the ship computer doesn't remember whether the missing Historian is trapped in the area containing a giant electromagnet or molten lava. You'll need to make sure that for each of the five codes, you find the shortest sequence of button presses necessary. The complexity of a single code (like 029A) is equal to the result of multiplying these two values: The length of the shortest sequence of button presses you need to type on your directional keypad in order to cause the code to be typed on the numeric keypad; for 029A, this would be 68. The numeric part of the code (ignoring leading zeroes); for 029A, this would be 29. In the above example, complexity of the five codes can be found by calculating 68 * 29, 60 * 980, 68 * 179, 64 * 456, and 64 * 379. Adding these together produces 126384. Find the fewest number of button presses you'll need to perform in order to cause the robot in front of the door to type each code. What is the sum of the complexities of the five codes on your list? Your puzzle answer was 211930. The first half of this puzzle is complete! It provides one gold star: * --- Part Two --- Just as the missing Historian is released, The Historians realize that a second member of their search party has also been missing this entire time! A quick life-form scan reveals the Historian is also trapped in a locked area of the ship. Due to a variety of hazards, robots are once again dispatched, forming another chain of remote control keypads managing robotic-arm-wielding robots. This time, many more robots are involved. In summary, there are the following keypads: One directional keypad that you are using. 25 directional keypads that robots are using. One numeric keypad (on a door) that a robot is using. The keypads form a chain, just like before: your directional keypad controls a robot which is typing on a directional keypad which controls a robot which is typing on a directional keypad... and so on, ending with the robot which is typing on the numeric keypad. The door codes are the same this time around; only the number of robots and directional keypads has changed. Find the fewest number of button presses you'll need to perform in order to cause the robot in front of the door to type each code. What is the sum of the complexities of the five codes on your list?	10
--- Day 16: Flawed Frequency Transmission --- You're 3/4ths of the way through the gas giants. Not only do roundtrip signals to Earth take five hours, but the signal quality is quite bad as well. You can clean up the signal with the Flawed Frequency Transmission algorithm, or FFT. As input, FFT takes a list of numbers. In the signal you received (your puzzle input), each number is a single digit: data like 15243 represents the sequence 1, 5, 2, 4, 3. FFT operates in repeated phases. In each phase, a new list is constructed with the same length as the input list. This new list is also used as the input for the next phase. Each element in the new list is built by multiplying every value in the input list by a value in a repeating pattern and then adding up the results. So, if the input list were 9, 8, 7, 6, 5 and the pattern for a given element were 1, 2, 3, the result would be 91 + 82 + 73 + 61 + 52 (with each input element on the left and each value in the repeating pattern on the right of each multiplication). Then, only the ones digit is kept: 38 becomes 8, -17 becomes 7, and so on. While each element in the output array uses all of the same input array elements, the actual repeating pattern to use depends on which output element is being calculated. The base pattern is 0, 1, 0, -1. Then, repeat each value in the pattern a number of times equal to the position in the output list being considered. Repeat once for the first element, twice for the second element, three times for the third element, and so on. So, if the third element of the output list is being calculated, repeating the values would produce: 0, 0, 0, 1, 1, 1, 0, 0, 0, -1, -1, -1. When applying the pattern, skip the very first value exactly once. (In other words, offset the whole pattern left by one.) So, for the second element of the output list, the actual pattern used would be: 0, 1, 1, 0, 0, -1, -1, 0, 0, 1, 1, 0, 0, -1, -1, .... After using this process to calculate each element of the output list, the phase is complete, and the output list of this phase is used as the new input list for the next phase, if any. Given the input signal 12345678, below are four phases of FFT. Within each phase, each output digit is calculated on a single line with the result at the far right; each multiplication operation shows the input digit on the left and the pattern value on the right: Input signal: 12345678 11 + 20 + 3-1 + 40 + 51 + 60 + 7-1 + 80 = 4 10 + 21 + 31 + 40 + 50 + 6-1 + 7-1 + 80 = 8 10 + 20 + 31 + 41 + 51 + 60 + 70 + 80 = 2 10 + 20 + 30 + 41 + 51 + 61 + 71 + 80 = 2 10 + 20 + 30 + 40 + 51 + 61 + 71 + 81 = 6 10 + 20 + 30 + 40 + 50 + 61 + 71 + 81 = 1 10 + 20 + 30 + 40 + 50 + 60 + 71 + 81 = 5 10 + 20 + 30 + 40 + 50 + 60 + 70 + 81 = 8 After 1 phase: 48226158 41 + 80 + 2-1 + 20 + 61 + 10 + 5-1 + 80 = 3 40 + 81 + 21 + 20 + 60 + 1-1 + 5-1 + 80 = 4 40 + 80 + 21 + 21 + 61 + 10 + 50 + 80 = 0 40 + 80 + 20 + 21 + 61 + 11 + 51 + 80 = 4 40 + 80 + 20 + 20 + 61 + 11 + 51 + 81 = 0 40 + 80 + 20 + 20 + 60 + 11 + 51 + 81 = 4 40 + 80 + 20 + 20 + 60 + 10 + 51 + 81 = 3 40 + 80 + 20 + 20 + 60 + 10 + 50 + 81 = 8 After 2 phases: 34040438 31 + 40 + 0-1 + 40 + 01 + 40 + 3-1 + 80 = 0 30 + 41 + 01 + 40 + 00 + 4-1 + 3-1 + 80 = 3 30 + 40 + 01 + 41 + 01 + 40 + 30 + 80 = 4 30 + 40 + 00 + 41 + 01 + 41 + 31 + 80 = 1 30 + 40 + 00 + 40 + 01 + 41 + 31 + 81 = 5 30 + 40 + 00 + 40 + 00 + 41 + 31 + 81 = 5 30 + 40 + 00 + 40 + 00 + 40 + 31 + 81 = 1 30 + 40 + 00 + 40 + 00 + 40 + 30 + 81 = 8 After 3 phases: 03415518 01 + 30 + 4-1 + 10 + 51 + 50 + 1-1 + 80 = 0 00 + 31 + 41 + 10 + 50 + 5-1 + 1-1 + 80 = 1 00 + 30 + 41 + 11 + 51 + 50 + 10 + 80 = 0 00 + 30 + 40 + 11 + 51 + 51 + 11 + 80 = 2 00 + 30 + 40 + 10 + 51 + 51 + 11 + 81 = 9 00 + 30 + 40 + 10 + 50 + 51 + 11 + 81 = 4 00 + 30 + 40 + 10 + 50 + 50 + 11 + 81 = 9 00 + 30 + 40 + 10 + 50 + 50 + 10 + 8*1 = 8 After 4 phases: 01029498 Here are the first eight digits of the final output list after 100 phases for some larger inputs: 80871224585914546619083218645595 becomes 24176176. 19617804207202209144916044189917 becomes 73745418. 69317163492948606335995924319873 becomes 52432133. After 100 phases of FFT, what are the first eight digits in the final output list?	11
--- Day 10: Monitoring Station --- You fly into the asteroid belt and reach the Ceres monitoring station. The Elves here have an emergency: they're having trouble tracking all of the asteroids and can't be sure they're safe. The Elves would like to build a new monitoring station in a nearby area of space; they hand you a map of all of the asteroids in that region (your puzzle input). The map indicates whether each position is empty (.) or contains an asteroid (#). The asteroids are much smaller than they appear on the map, and every asteroid is exactly in the center of its marked position. The asteroids can be described with X,Y coordinates where X is the distance from the left edge and Y is the distance from the top edge (so the top-left corner is 0,0 and the position immediately to its right is 1,0). Your job is to figure out which asteroid would be the best place to build a new monitoring station. A monitoring station can detect any asteroid to which it has direct line of sight - that is, there cannot be another asteroid exactly between them. This line of sight can be at any angle, not just lines aligned to the grid or diagonally. The best location is the asteroid that can detect the largest number of other asteroids. For example, consider the following map: .#..# ..... ##### ....# ...## The best location for a new monitoring station on this map is the highlighted asteroid at 3,4 because it can detect 8 asteroids, more than any other location. (The only asteroid it cannot detect is the one at 1,0; its view of this asteroid is blocked by the asteroid at 2,2.) All other asteroids are worse locations; they can detect 7 or fewer other asteroids. Here is the number of other asteroids a monitoring station on each asteroid could detect: .7..7 ..... 67775 ....7 ...87 Here is an asteroid (#) and some examples of the ways its line of sight might be blocked. If there were another asteroid at the location of a capital letter, the locations marked with the corresponding lowercase letter would be blocked and could not be detected: #......... ...A...... ...B..a... .EDCG....a ..F.c.b... .....c.... ..efd.c.gb .......c.. ....f...c. ...e..d..c Here are some larger examples: Best is 5,8 with 33 other asteroids detected: ......#.#. #..#.#.... ..#######. .#.#.###.. .#..#..... ..#....#.# #..#....#. .##.#..### ##...#..#. .#....#### Best is 1,2 with 35 other asteroids detected: #.#...#.#. .###....#. .#....#... ##.#.#.#.# ....#.#.#. .##..###.# ..#...##.. ..##....## ......#... .####.###. Best is 6,3 with 41 other asteroids detected: .#..#..### ####.###.# ....###.#. ..###.##.# ##.##.#.#. ....###..# ..#.#..#.# #..#.#.### .##...##.# .....#.#.. Best is 11,13 with 210 other asteroids detected: .#..##.###...####### ##.############..##. .#.######.########.# .###.#######.####.#. #####.##.#.##.###.## ..#####..#.######### #################### #.####....###.#.#.## ##.################# #####.##.###..####.. ..######..##.####### ####.##.####...##..# .#####..#.######.### ##...#.##########... #.##########.####### .####.#.###.###.#.## ....##.##.###..##### .#.#.###########.### #.#.#.#####.####.### ###.##.####.##.#..## Find the best location for a new monitoring station. How many other asteroids can be detected from that location?	12
--- Day 8: Seven Segment Search --- You barely reach the safety of the cave when the whale smashes into the cave mouth, collapsing it. Sensors indicate another exit to this cave at a much greater depth, so you have no choice but to press on. As your submarine slowly makes its way through the cave system, you notice that the four-digit seven-segment displays in your submarine are malfunctioning; they must have been damaged during the escape. You'll be in a lot of trouble without them, so you'd better figure out what's wrong. Each digit of a seven-segment display is rendered by turning on or off any of seven segments named a through g: 0: 1: 2: 3: 4: aaaa .... aaaa aaaa .... b c . c . c . c b c b c . c . c . c b c .... .... dddd dddd dddd e f . f e . . f . f e f . f e . . f . f gggg .... gggg gggg .... 5: 6: 7: 8: 9: aaaa aaaa aaaa aaaa aaaa b . b . . c b c b c b . b . . c b c b c dddd dddd .... dddd dddd . f e f . f e f . f . f e f . f e f . f gggg gggg .... gggg gggg So, to render a 1, only segments c and f would be turned on; the rest would be off. To render a 7, only segments a, c, and f would be turned on. The problem is that the signals which control the segments have been mixed up on each display. The submarine is still trying to display numbers by producing output on signal wires a through g, but those wires are connected to segments randomly. Worse, the wire/segment connections are mixed up separately for each four-digit display! (All of the digits within a display use the same connections, though.) So, you might know that only signal wires b and g are turned on, but that doesn't mean segments b and g are turned on: the only digit that uses two segments is 1, so it must mean segments c and f are meant to be on. With just that information, you still can't tell which wire (b/g) goes to which segment (c/f). For that, you'll need to collect more information. For each display, you watch the changing signals for a while, make a note of all ten unique signal patterns you see, and then write down a single four digit output value (your puzzle input). Using the signal patterns, you should be able to work out which pattern corresponds to which digit. For example, here is what you might see in a single entry in your notes: acedgfb cdfbe gcdfa fbcad dab cefabd cdfgeb eafb cagedb ab \| cdfeb fcadb cdfeb cdbaf (The entry is wrapped here to two lines so it fits; in your notes, it will all be on a single line.) Each entry consists of ten unique signal patterns, a \| delimiter, and finally the four digit output value. Within an entry, the same wire/segment connections are used (but you don't know what the connections actually are). The unique signal patterns correspond to the ten different ways the submarine tries to render a digit using the current wire/segment connections. Because 7 is the only digit that uses three segments, dab in the above example means that to render a 7, signal lines d, a, and b are on. Because 4 is the only digit that uses four segments, eafb means that to render a 4, signal lines e, a, f, and b are on. Using this information, you should be able to work out which combination of signal wires corresponds to each of the ten digits. Then, you can decode the four digit output value. Unfortunately, in the above example, all of the digits in the output value (cdfeb fcadb cdfeb cdbaf) use five segments and are more difficult to deduce. For now, focus on the easy digits. Consider this larger example: be cfbegad cbdgef fgaecd cgeb fdcge agebfd fecdb fabcd edb \| fdgacbe cefdb cefbgd gcbe edbfga begcd cbg gc gcadebf fbgde acbgfd abcde gfcbed gfec \| fcgedb cgb dgebacf gc fgaebd cg bdaec gdafb agbcfd gdcbef bgcad gfac gcb cdgabef \| cg cg fdcagb cbg fbegcd cbd adcefb dageb afcb bc aefdc ecdab fgdeca fcdbega \| efabcd cedba gadfec cb aecbfdg fbg gf bafeg dbefa fcge gcbea fcaegb dgceab fcbdga \| gecf egdcabf bgf bfgea fgeab ca afcebg bdacfeg cfaedg gcfdb baec bfadeg bafgc acf \| gebdcfa ecba ca fadegcb dbcfg fgd bdegcaf fgec aegbdf ecdfab fbedc dacgb gdcebf gf \| cefg dcbef fcge gbcadfe bdfegc cbegaf gecbf dfcage bdacg ed bedf ced adcbefg gebcd \| ed bcgafe cdgba cbgef egadfb cdbfeg cegd fecab cgb gbdefca cg fgcdab egfdb bfceg \| gbdfcae bgc cg cgb gcafb gcf dcaebfg ecagb gf abcdeg gaef cafbge fdbac fegbdc \| fgae cfgab fg bagce Because the digits 1, 4, 7, and 8 each use a unique number of segments, you should be able to tell which combinations of signals correspond to those digits. Counting only digits in the output values (the part after \| on each line), in the above example, there are 26 instances of digits that use a unique number of segments (highlighted above). In the output values, how many times do digits 1, 4, 7, or 8 appear?	13
--- Day 18: RAM Run --- You and The Historians look a lot more pixelated than you remember. You're inside a computer at the North Pole! Just as you're about to check out your surroundings, a program runs up to you. "This region of memory isn't safe! The User misunderstood what a pushdown automaton is and their algorithm is pushing whole bytes down on top of us! Run!" The algorithm is fast - it's going to cause a byte to fall into your memory space once every nanosecond! Fortunately, you're faster, and by quickly scanning the algorithm, you create a list of which bytes will fall (your puzzle input) in the order they'll land in your memory space. Your memory space is a two-dimensional grid with coordinates that range from 0 to 70 both horizontally and vertically. However, for the sake of example, suppose you're on a smaller grid with coordinates that range from 0 to 6 and the following list of incoming byte positions: 5,4 4,2 4,5 3,0 2,1 6,3 2,4 1,5 0,6 3,3 2,6 5,1 1,2 5,5 2,5 6,5 1,4 0,4 6,4 1,1 6,1 1,0 0,5 1,6 2,0 Each byte position is given as an X,Y coordinate, where X is the distance from the left edge of your memory space and Y is the distance from the top edge of your memory space. You and The Historians are currently in the top left corner of the memory space (at 0,0) and need to reach the exit in the bottom right corner (at 70,70 in your memory space, but at 6,6 in this example). You'll need to simulate the falling bytes to plan out where it will be safe to run; for now, simulate just the first few bytes falling into your memory space. As bytes fall into your memory space, they make that coordinate corrupted. Corrupted memory coordinates cannot be entered by you or The Historians, so you'll need to plan your route carefully. You also cannot leave the boundaries of the memory space; your only hope is to reach the exit. In the above example, if you were to draw the memory space after the first 12 bytes have fallen (using . for safe and # for corrupted), it would look like this: ...#... ..#..#. ....#.. ...#..# ..#..#. .#..#.. #.#.... You can take steps up, down, left, or right. After just 12 bytes have corrupted locations in your memory space, the shortest path from the top left corner to the exit would take 22 steps. Here (marked with O) is one such path: OO.#OOO .O#OO#O .OOO#OO ...#OO# ..#OO#. .#.O#.. #.#OOOO Simulate the first kilobyte (1024 bytes) falling onto your memory space. Afterward, what is the minimum number of steps needed to reach the exit? Your puzzle answer was 354. The first half of this puzzle is complete! It provides one gold star: * --- Part Two --- The Historians aren't as used to moving around in this pixelated universe as you are. You're afraid they're not going to be fast enough to make it to the exit before the path is completely blocked. To determine how fast everyone needs to go, you need to determine the first byte that will cut off the path to the exit. In the above example, after the byte at 1,1 falls, there is still a path to the exit: O..#OOO O##OO#O O#OO#OO OOO#OO# ###OO## .##O### #.#OOOO However, after adding the very next byte (at 6,1), there is no longer a path to the exit: ...#... .##..## .#..#.. ...#..# ###..## .##.### #.#.... So, in this example, the coordinates of the first byte that prevents the exit from being reachable are 6,1. Simulate more of the bytes that are about to corrupt your memory space. What are the coordinates of the first byte that will prevent the exit from being reachable from your starting position? (Provide the answer as two integers separated by a comma with no other characters.)	14
--- Day 18: RAM Run --- You and The Historians look a lot more pixelated than you remember. You're inside a computer at the North Pole! Just as you're about to check out your surroundings, a program runs up to you. "This region of memory isn't safe! The User misunderstood what a pushdown automaton is and their algorithm is pushing whole bytes down on top of us! Run!" The algorithm is fast - it's going to cause a byte to fall into your memory space once every nanosecond! Fortunately, you're faster, and by quickly scanning the algorithm, you create a list of which bytes will fall (your puzzle input) in the order they'll land in your memory space. Your memory space is a two-dimensional grid with coordinates that range from 0 to 70 both horizontally and vertically. However, for the sake of example, suppose you're on a smaller grid with coordinates that range from 0 to 6 and the following list of incoming byte positions: 5,4 4,2 4,5 3,0 2,1 6,3 2,4 1,5 0,6 3,3 2,6 5,1 1,2 5,5 2,5 6,5 1,4 0,4 6,4 1,1 6,1 1,0 0,5 1,6 2,0 Each byte position is given as an X,Y coordinate, where X is the distance from the left edge of your memory space and Y is the distance from the top edge of your memory space. You and The Historians are currently in the top left corner of the memory space (at 0,0) and need to reach the exit in the bottom right corner (at 70,70 in your memory space, but at 6,6 in this example). You'll need to simulate the falling bytes to plan out where it will be safe to run; for now, simulate just the first few bytes falling into your memory space. As bytes fall into your memory space, they make that coordinate corrupted. Corrupted memory coordinates cannot be entered by you or The Historians, so you'll need to plan your route carefully. You also cannot leave the boundaries of the memory space; your only hope is to reach the exit. In the above example, if you were to draw the memory space after the first 12 bytes have fallen (using . for safe and # for corrupted), it would look like this: ...#... ..#..#. ....#.. ...#..# ..#..#. .#..#.. #.#.... You can take steps up, down, left, or right. After just 12 bytes have corrupted locations in your memory space, the shortest path from the top left corner to the exit would take 22 steps. Here (marked with O) is one such path: OO.#OOO .O#OO#O .OOO#OO ...#OO# ..#OO#. .#.O#.. #.#OOOO Simulate the first kilobyte (1024 bytes) falling onto your memory space. Afterward, what is the minimum number of steps needed to reach the exit?	15
--- Day 9: Encoding Error --- With your neighbor happily enjoying their video game, you turn your attention to an open data port on the little screen in the seat in front of you. Though the port is non-standard, you manage to connect it to your computer through the clever use of several paperclips. Upon connection, the port outputs a series of numbers (your puzzle input). The data appears to be encrypted with the eXchange-Masking Addition System (XMAS) which, conveniently for you, is an old cypher with an important weakness. XMAS starts by transmitting a preamble of 25 numbers. After that, each number you receive should be the sum of any two of the 25 immediately previous numbers. The two numbers will have different values, and there might be more than one such pair. For example, suppose your preamble consists of the numbers 1 through 25 in a random order. To be valid, the next number must be the sum of two of those numbers: 26 would be a valid next number, as it could be 1 plus 25 (or many other pairs, like 2 and 24). 49 would be a valid next number, as it is the sum of 24 and 25. 100 would not be valid; no two of the previous 25 numbers sum to 100. 50 would also not be valid; although 25 appears in the previous 25 numbers, the two numbers in the pair must be different. Suppose the 26th number is 45, and the first number (no longer an option, as it is more than 25 numbers ago) was 20. Now, for the next number to be valid, there needs to be some pair of numbers among 1-19, 21-25, or 45 that add up to it: 26 would still be a valid next number, as 1 and 25 are still within the previous 25 numbers. 65 would not be valid, as no two of the available numbers sum to it. 64 and 66 would both be valid, as they are the result of 19+45 and 21+45 respectively. Here is a larger example which only considers the previous 5 numbers (and has a preamble of length 5): 35 20 15 25 47 40 62 55 65 95 102 117 150 182 127 219 299 277 309 576 In this example, after the 5-number preamble, almost every number is the sum of two of the previous 5 numbers; the only number that does not follow this rule is 127. The first step of attacking the weakness in the XMAS data is to find the first number in the list (after the preamble) which is not the sum of two of the 25 numbers before it. What is the first number that does not have this property?	16
--- Day 1: No Time for a Taxicab --- Santa's sleigh uses a very high-precision clock to guide its movements, and the clock's oscillator is regulated by stars. Unfortunately, the stars have been stolen... by the Easter Bunny. To save Christmas, Santa needs you to retrieve all fifty stars by December 25th. Collect stars by solving puzzles. Two puzzles will be made available on each day in the Advent calendar; the second puzzle is unlocked when you complete the first. Each puzzle grants one star. Good luck! You're airdropped near Easter Bunny Headquarters in a city somewhere. "Near", unfortunately, is as close as you can get - the instructions on the Easter Bunny Recruiting Document the Elves intercepted start here, and nobody had time to work them out further. The Document indicates that you should start at the given coordinates (where you just landed) and face North. Then, follow the provided sequence: either turn left (L) or right (R) 90 degrees, then walk forward the given number of blocks, ending at a new intersection. There's no time to follow such ridiculous instructions on foot, though, so you take a moment and work out the destination. Given that you can only walk on the street grid of the city, how far is the shortest path to the destination? For example: Following R2, L3 leaves you 2 blocks East and 3 blocks North, or 5 blocks away. R2, R2, R2 leaves you 2 blocks due South of your starting position, which is 2 blocks away. R5, L5, R5, R3 leaves you 12 blocks away. How many blocks away is Easter Bunny HQ?	17
--- Day 6: Chronal Coordinates --- The device on your wrist beeps several times, and once again you feel like you're falling. "Situation critical," the device announces. "Destination indeterminate. Chronal interference detected. Please specify new target coordinates." The device then produces a list of coordinates (your puzzle input). Are they places it thinks are safe or dangerous? It recommends you check manual page 729. The Elves did not give you a manual. If they're dangerous, maybe you can minimize the danger by finding the coordinate that gives the largest distance from the other points. Using only the Manhattan distance, determine the area around each coordinate by counting the number of integer X,Y locations that are closest to that coordinate (and aren't tied in distance to any other coordinate). Your goal is to find the size of the largest area that isn't infinite. For example, consider the following list of coordinates: 1, 1 1, 6 8, 3 3, 4 5, 5 8, 9 If we name these coordinates A through F, we can draw them on a grid, putting 0,0 at the top left: .......... .A........ .......... ........C. ...D...... .....E.... .B........ .......... .......... ........F. This view is partial - the actual grid extends infinitely in all directions. Using the Manhattan distance, each location's closest coordinate can be determined, shown here in lowercase: aaaaa.cccc aAaaa.cccc aaaddecccc aadddeccCc ..dDdeeccc bb.deEeecc bBb.eeee.. bbb.eeefff bbb.eeffff bbb.ffffFf Locations shown as . are equally far from two or more coordinates, and so they don't count as being closest to any. In this example, the areas of coordinates A, B, C, and F are infinite - while not shown here, their areas extend forever outside the visible grid. However, the areas of coordinates D and E are finite: D is closest to 9 locations, and E is closest to 17 (both including the coordinate's location itself). Therefore, in this example, the size of the largest area is 17. What is the size of the largest area that isn't infinite?	18
--- Day 5: Alchemical Reduction --- You've managed to sneak in to the prototype suit manufacturing lab. The Elves are making decent progress, but are still struggling with the suit's size reduction capabilities. While the very latest in 1518 alchemical technology might have solved their problem eventually, you can do better. You scan the chemical composition of the suit's material and discover that it is formed by extremely long polymers (one of which is available as your puzzle input). The polymer is formed by smaller units which, when triggered, react with each other such that two adjacent units of the same type and opposite polarity are destroyed. Units' types are represented by letters; units' polarity is represented by capitalization. For instance, r and R are units with the same type but opposite polarity, whereas r and s are entirely different types and do not react. For example: In aA, a and A react, leaving nothing behind. In abBA, bB destroys itself, leaving aA. As above, this then destroys itself, leaving nothing. In abAB, no two adjacent units are of the same type, and so nothing happens. In aabAAB, even though aa and AA are of the same type, their polarities match, and so nothing happens. Now, consider a larger example, dabAcCaCBAcCcaDA: dabAcCaCBAcCcaDA The first 'cC' is removed. dabAaCBAcCcaDA This creates 'Aa', which is removed. dabCBAcCcaDA Either 'cC' or 'Cc' are removed (the result is the same). dabCBAcaDA No further actions can be taken. After all possible reactions, the resulting polymer contains 10 units. How many units remain after fully reacting the polymer you scanned? (Note: in this puzzle and others, the input is large; if you copy/paste your input, make sure you get the whole thing.) Your puzzle answer was 11636. --- Part Two --- Time to improve the polymer. One of the unit types is causing problems; it's preventing the polymer from collapsing as much as it should. Your goal is to figure out which unit type is causing the most problems, remove all instances of it (regardless of polarity), fully react the remaining polymer, and measure its length. For example, again using the polymer dabAcCaCBAcCcaDA from above: Removing all A/a units produces dbcCCBcCcD. Fully reacting this polymer produces dbCBcD, which has length 6. Removing all B/b units produces daAcCaCAcCcaDA. Fully reacting this polymer produces daCAcaDA, which has length 8. Removing all C/c units produces dabAaBAaDA. Fully reacting this polymer produces daDA, which has length 4. Removing all D/d units produces abAcCaCBAcCcaA. Fully reacting this polymer produces abCBAc, which has length 6. In this example, removing all C/c units was best, producing the answer 4. What is the length of the shortest polymer you can produce by removing all units of exactly one type and fully reacting the result?	19
--- Day 24: Crossed Wires --- You and The Historians arrive at the edge of a large grove somewhere in the jungle. After the last incident, the Elves installed a small device that monitors the fruit. While The Historians search the grove, one of them asks if you can take a look at the monitoring device; apparently, it's been malfunctioning recently. The device seems to be trying to produce a number through some boolean logic gates. Each gate has two inputs and one output. The gates all operate on values that are either true (1) or false (0). AND gates output 1 if both inputs are 1; if either input is 0, these gates output 0. OR gates output 1 if one or both inputs is 1; if both inputs are 0, these gates output 0. XOR gates output 1 if the inputs are different; if the inputs are the same, these gates output 0. Gates wait until both inputs are received before producing output; wires can carry 0, 1 or no value at all. There are no loops; once a gate has determined its output, the output will not change until the whole system is reset. Each wire is connected to at most one gate output, but can be connected to many gate inputs. Rather than risk getting shocked while tinkering with the live system, you write down all of the gate connections and initial wire values (your puzzle input) so you can consider them in relative safety. For example: x00: 1 x01: 1 x02: 1 y00: 0 y01: 1 y02: 0 x00 AND y00 -> z00 x01 XOR y01 -> z01 x02 OR y02 -> z02 Because gates wait for input, some wires need to start with a value (as inputs to the entire system). The first section specifies these values. For example, x00: 1 means that the wire named x00 starts with the value 1 (as if a gate is already outputting that value onto that wire). The second section lists all of the gates and the wires connected to them. For example, x00 AND y00 -> z00 describes an instance of an AND gate which has wires x00 and y00 connected to its inputs and which will write its output to wire z00. In this example, simulating these gates eventually causes 0 to appear on wire z00, 0 to appear on wire z01, and 1 to appear on wire z02. Ultimately, the system is trying to produce a number by combining the bits on all wires starting with z. z00 is the least significant bit, then z01, then z02, and so on. In this example, the three output bits form the binary number 100 which is equal to the decimal number 4. Here's a larger example: x00: 1 x01: 0 x02: 1 x03: 1 x04: 0 y00: 1 y01: 1 y02: 1 y03: 1 y04: 1 ntg XOR fgs -> mjb y02 OR x01 -> tnw kwq OR kpj -> z05 x00 OR x03 -> fst tgd XOR rvg -> z01 vdt OR tnw -> bfw bfw AND frj -> z10 ffh OR nrd -> bqk y00 AND y03 -> djm y03 OR y00 -> psh bqk OR frj -> z08 tnw OR fst -> frj gnj AND tgd -> z11 bfw XOR mjb -> z00 x03 OR x00 -> vdt gnj AND wpb -> z02 x04 AND y00 -> kjc djm OR pbm -> qhw nrd AND vdt -> hwm kjc AND fst -> rvg y04 OR y02 -> fgs y01 AND x02 -> pbm ntg OR kjc -> kwq psh XOR fgs -> tgd qhw XOR tgd -> z09 pbm OR djm -> kpj x03 XOR y03 -> ffh x00 XOR y04 -> ntg bfw OR bqk -> z06 nrd XOR fgs -> wpb frj XOR qhw -> z04 bqk OR frj -> z07 y03 OR x01 -> nrd hwm AND bqk -> z03 tgd XOR rvg -> z12 tnw OR pbm -> gnj After waiting for values on all wires starting with z, the wires in this system have the following values: bfw: 1 bqk: 1 djm: 1 ffh: 0 fgs: 1 frj: 1 fst: 1 gnj: 1 hwm: 1 kjc: 0 kpj: 1 kwq: 0 mjb: 1 nrd: 1 ntg: 0 pbm: 1 psh: 1 qhw: 1 rvg: 0 tgd: 0 tnw: 1 vdt: 1 wpb: 0 z00: 0 z01: 0 z02: 0 z03: 1 z04: 0 z05: 1 z06: 1 z07: 1 z08: 1 z09: 1 z10: 1 z11: 0 z12: 0 Combining the bits from all wires starting with z produces the binary number 0011111101000. Converting this number to decimal produces 2024. Simulate the system of gates and wires. What decimal number does it output on the wires starting with z?	20
--- Day 6: Universal Orbit Map --- You've landed at the Universal Orbit Map facility on Mercury. Because navigation in space often involves transferring between orbits, the orbit maps here are useful for finding efficient routes between, for example, you and Santa. You download a map of the local orbits (your puzzle input). Except for the universal Center of Mass (COM), every object in space is in orbit around exactly one other object. An orbit looks roughly like this: \| \| AAA--> o o <--BBB \| \| / / In this diagram, the object BBB is in orbit around AAA. The path that BBB takes around AAA (drawn with lines) is only partly shown. In the map data, this orbital relationship is written AAA)BBB, which means "BBB is in orbit around AAA". Before you use your map data to plot a course, you need to make sure it wasn't corrupted during the download. To verify maps, the Universal Orbit Map facility uses orbit count checksums - the total number of direct orbits (like the one shown above) and indirect orbits. Whenever A orbits B and B orbits C, then A indirectly orbits C. This chain can be any number of objects long: if A orbits B, B orbits C, and C orbits D, then A indirectly orbits D. For example, suppose you have the following map: COM)B B)C C)D D)E E)F B)G G)H D)I E)J J)K K)L Visually, the above map of orbits looks like this: G - H J - K - L / / COM - B - C - D - E - F I In this visual representation, when two objects are connected by a line, the one on the right directly orbits the one on the left. Here, we can count the total number of orbits as follows: D directly orbits C and indirectly orbits B and COM, a total of 3 orbits. L directly orbits K and indirectly orbits J, E, D, C, B, and COM, a total of 7 orbits. COM orbits nothing. The total number of direct and indirect orbits in this example is 42. What is the total number of direct and indirect orbits in your map data? Your puzzle answer was 160040. --- Part Two --- Now, you just need to figure out how many orbital transfers you (YOU) need to take to get to Santa (SAN). You start at the object YOU are orbiting; your destination is the object SAN is orbiting. An orbital transfer lets you move from any object to an object orbiting or orbited by that object. For example, suppose you have the following map: COM)B B)C C)D D)E E)F B)G G)H D)I E)J J)K K)L K)YOU I)SAN Visually, the above map of orbits looks like this: YOU / G - H J - K - L / / COM - B - C - D - E - F I - SAN In this example, YOU are in orbit around K, and SAN is in orbit around I. To move from K to I, a minimum of 4 orbital transfers are required: K to J J to E E to D D to I Afterward, the map of orbits looks like this: G - H J - K - L / / COM - B - C - D - E - F I - SAN YOU What is the minimum number of orbital transfers required to move from the object YOU are orbiting to the object SAN is orbiting? (Between the objects they are orbiting - not between YOU and SAN.)	21
--- Day 10: Cathode-Ray Tube --- You avoid the ropes, plunge into the river, and swim to shore. The Elves yell something about meeting back up with them upriver, but the river is too loud to tell exactly what they're saying. They finish crossing the bridge and disappear from view. Situations like this must be why the Elves prioritized getting the communication system on your handheld device working. You pull it out of your pack, but the amount of water slowly draining from a big crack in its screen tells you it probably won't be of much immediate use. Unless, that is, you can design a replacement for the device's video system! It seems to be some kind of cathode-ray tube screen and simple CPU that are both driven by a precise clock circuit. The clock circuit ticks at a constant rate; each tick is called a cycle. Start by figuring out the signal being sent by the CPU. The CPU has a single register, X, which starts with the value 1. It supports only two instructions: addx V takes two cycles to complete. After two cycles, the X register is increased by the value V. (V can be negative.) noop takes one cycle to complete. It has no other effect. The CPU uses these instructions in a program (your puzzle input) to, somehow, tell the screen what to draw. Consider the following small program: noop addx 3 addx -5 Execution of this program proceeds as follows: At the start of the first cycle, the noop instruction begins execution. During the first cycle, X is 1. After the first cycle, the noop instruction finishes execution, doing nothing. At the start of the second cycle, the addx 3 instruction begins execution. During the second cycle, X is still 1. During the third cycle, X is still 1. After the third cycle, the addx 3 instruction finishes execution, setting X to 4. At the start of the fourth cycle, the addx -5 instruction begins execution. During the fourth cycle, X is still 4. During the fifth cycle, X is still 4. After the fifth cycle, the addx -5 instruction finishes execution, setting X to -1. Maybe you can learn something by looking at the value of the X register throughout execution. For now, consider the signal strength (the cycle number multiplied by the value of the X register) during the 20th cycle and every 40 cycles after that (that is, during the 20th, 60th, 100th, 140th, 180th, and 220th cycles). For example, consider this larger program: addx 15 addx -11 addx 6 addx -3 addx 5 addx -1 addx -8 addx 13 addx 4 noop addx -1 addx 5 addx -1 addx 5 addx -1 addx 5 addx -1 addx 5 addx -1 addx -35 addx 1 addx 24 addx -19 addx 1 addx 16 addx -11 noop noop addx 21 addx -15 noop noop addx -3 addx 9 addx 1 addx -3 addx 8 addx 1 addx 5 noop noop noop noop noop addx -36 noop addx 1 addx 7 noop noop noop addx 2 addx 6 noop noop noop noop noop addx 1 noop noop addx 7 addx 1 noop addx -13 addx 13 addx 7 noop addx 1 addx -33 noop noop noop addx 2 noop noop noop addx 8 noop addx -1 addx 2 addx 1 noop addx 17 addx -9 addx 1 addx 1 addx -3 addx 11 noop noop addx 1 noop addx 1 noop noop addx -13 addx -19 addx 1 addx 3 addx 26 addx -30 addx 12 addx -1 addx 3 addx 1 noop noop noop addx -9 addx 18 addx 1 addx 2 noop noop addx 9 noop noop noop addx -1 addx 2 addx -37 addx 1 addx 3 noop addx 15 addx -21 addx 22 addx -6 addx 1 noop addx 2 addx 1 noop addx -10 noop noop addx 20 addx 1 addx 2 addx 2 addx -6 addx -11 noop noop noop The interesting signal strengths can be determined as follows: During the 20th cycle, register X has the value 21, so the signal strength is 20 * 21 = 420. (The 20th cycle occurs in the middle of the second addx -1, so the value of register X is the starting value, 1, plus all of the other addx values up to that point: 1 + 15 - 11 + 6 - 3 + 5 - 1 - 8 + 13 + 4 = 21.) During the 60th cycle, register X has the value 19, so the signal strength is 60 * 19 = 1140. During the 100th cycle, register X has the value 18, so the signal strength is 100 * 18 = 1800. During the 140th cycle, register X has the value 21, so the signal strength is 140 * 21 = 2940. During the 180th cycle, register X has the value 16, so the signal strength is 180 * 16 = 2880. During the 220th cycle, register X has the value 18, so the signal strength is 220 * 18 = 3960. The sum of these signal strengths is 13140. Find the signal strength during the 20th, 60th, 100th, 140th, 180th, and 220th cycles. What is the sum of these six signal strengths?	22
--- Day 17: Spinlock --- Suddenly, whirling in the distance, you notice what looks like a massive, pixelated hurricane: a deadly spinlock. This spinlock isn't just consuming computing power, but memory, too; vast, digital mountains are being ripped from the ground and consumed by the vortex. If you don't move quickly, fixing that printer will be the least of your problems. This spinlock's algorithm is simple but efficient, quickly consuming everything in its path. It starts with a circular buffer containing only the value 0, which it marks as the current position. It then steps forward through the circular buffer some number of steps (your puzzle input) before inserting the first new value, 1, after the value it stopped on. The inserted value becomes the current position. Then, it steps forward from there the same number of steps, and wherever it stops, inserts after it the second new value, 2, and uses that as the new current position again. It repeats this process of stepping forward, inserting a new value, and using the location of the inserted value as the new current position a total of 2017 times, inserting 2017 as its final operation, and ending with a total of 2018 values (including 0) in the circular buffer. For example, if the spinlock were to step 3 times per insert, the circular buffer would begin to evolve like this (using parentheses to mark the current position after each iteration of the algorithm): (0), the initial state before any insertions. 0 (1): the spinlock steps forward three times (0, 0, 0), and then inserts the first value, 1, after it. 1 becomes the current position. 0 (2) 1: the spinlock steps forward three times (0, 1, 0), and then inserts the second value, 2, after it. 2 becomes the current position. 0 2 (3) 1: the spinlock steps forward three times (1, 0, 2), and then inserts the third value, 3, after it. 3 becomes the current position. And so on: 0 2 (4) 3 1 0 (5) 2 4 3 1 0 5 2 4 3 (6) 1 0 5 (7) 2 4 3 6 1 0 5 7 2 4 3 (8) 6 1 0 (9) 5 7 2 4 3 8 6 1 Eventually, after 2017 insertions, the section of the circular buffer near the last insertion looks like this: 1512 1134 151 (2017) 638 1513 851 Perhaps, if you can identify the value that will ultimately be after the last value written (2017), you can short-circuit the spinlock. In this example, that would be 638. What is the value after 2017 in your completed circular buffer?	23
--- Day 6: Memory Reallocation --- A debugger program here is having an issue: it is trying to repair a memory reallocation routine, but it keeps getting stuck in an infinite loop. In this area, there are sixteen memory banks; each memory bank can hold any number of blocks. The goal of the reallocation routine is to balance the blocks between the memory banks. The reallocation routine operates in cycles. In each cycle, it finds the memory bank with the most blocks (ties won by the lowest-numbered memory bank) and redistributes those blocks among the banks. To do this, it removes all of the blocks from the selected bank, then moves to the next (by index) memory bank and inserts one of the blocks. It continues doing this until it runs out of blocks; if it reaches the last memory bank, it wraps around to the first one. The debugger would like to know how many redistributions can be done before a blocks-in-banks configuration is produced that has been seen before. For example, imagine a scenario with only four memory banks: The banks start with 0, 2, 7, and 0 blocks. The third bank has the most blocks, so it is chosen for redistribution. Starting with the next bank (the fourth bank) and then continuing to the first bank, the second bank, and so on, the 7 blocks are spread out over the memory banks. The fourth, first, and second banks get two blocks each, and the third bank gets one back. The final result looks like this: 2 4 1 2. Next, the second bank is chosen because it contains the most blocks (four). Because there are four memory banks, each gets one block. The result is: 3 1 2 3. Now, there is a tie between the first and fourth memory banks, both of which have three blocks. The first bank wins the tie, and its three blocks are distributed evenly over the other three banks, leaving it with none: 0 2 3 4. The fourth bank is chosen, and its four blocks are distributed such that each of the four banks receives one: 1 3 4 1. The third bank is chosen, and the same thing happens: 2 4 1 2. At this point, we've reached a state we've seen before: 2 4 1 2 was already seen. The infinite loop is detected after the fifth block redistribution cycle, and so the answer in this example is 5. Given the initial block counts in your puzzle input, how many redistribution cycles must be completed before a configuration is produced that has been seen before? Your puzzle answer was 12841. --- Part Two --- Out of curiosity, the debugger would also like to know the size of the loop: starting from a state that has already been seen, how many block redistribution cycles must be performed before that same state is seen again? In the example above, 2 4 1 2 is seen again after four cycles, and so the answer in that example would be 4. How many cycles are in the infinite loop that arises from the configuration in your puzzle input?	24
--- Day 24: Arithmetic Logic Unit --- Magic smoke starts leaking from the submarine's arithmetic logic unit (ALU). Without the ability to perform basic arithmetic and logic functions, the submarine can't produce cool patterns with its Christmas lights! It also can't navigate. Or run the oxygen system. Don't worry, though - you probably have enough oxygen left to give you enough time to build a new ALU. The ALU is a four-dimensional processing unit: it has integer variables w, x, y, and z. These variables all start with the value 0. The ALU also supports six instructions: inp a - Read an input value and write it to variable a. add a b - Add the value of a to the value of b, then store the result in variable a. mul a b - Multiply the value of a by the value of b, then store the result in variable a. div a b - Divide the value of a by the value of b, truncate the result to an integer, then store the result in variable a. (Here, "truncate" means to round the value toward zero.) mod a b - Divide the value of a by the value of b, then store the remainder in variable a. (This is also called the modulo operation.) eql a b - If the value of a and b are equal, then store the value 1 in variable a. Otherwise, store the value 0 in variable a. In all of these instructions, a and b are placeholders; a will always be the variable where the result of the operation is stored (one of w, x, y, or z), while b can be either a variable or a number. Numbers can be positive or negative, but will always be integers. The ALU has no jump instructions; in an ALU program, every instruction is run exactly once in order from top to bottom. The program halts after the last instruction has finished executing. (Program authors should be especially cautious; attempting to execute div with b=0 or attempting to execute mod with a<0 or b<=0 will cause the program to crash and might even damage the ALU. These operations are never intended in any serious ALU program.) For example, here is an ALU program which takes an input number, negates it, and stores it in x: inp x mul x -1 Here is an ALU program which takes two input numbers, then sets z to 1 if the second input number is three times larger than the first input number, or sets z to 0 otherwise: inp z inp x mul z 3 eql z x Here is an ALU program which takes a non-negative integer as input, converts it into binary, and stores the lowest (1's) bit in z, the second-lowest (2's) bit in y, the third-lowest (4's) bit in x, and the fourth-lowest (8's) bit in w: inp w add z w mod z 2 div w 2 add y w mod y 2 div w 2 add x w mod x 2 div w 2 mod w 2 Once you have built a replacement ALU, you can install it in the submarine, which will immediately resume what it was doing when the ALU failed: validating the submarine's model number. To do this, the ALU will run the MOdel Number Automatic Detector program (MONAD, your puzzle input). Submarine model numbers are always fourteen-digit numbers consisting only of digits 1 through 9. The digit 0 cannot appear in a model number. When MONAD checks a hypothetical fourteen-digit model number, it uses fourteen separate inp instructions, each expecting a single digit of the model number in order of most to least significant. (So, to check the model number 13579246899999, you would give 1 to the first inp instruction, 3 to the second inp instruction, 5 to the third inp instruction, and so on.) This means that when operating MONAD, each input instruction should only ever be given an integer value of at least 1 and at most 9. Then, after MONAD has finished running all of its instructions, it will indicate that the model number was valid by leaving a 0 in variable z. However, if the model number was invalid, it will leave some other non-zero value in z. MONAD imposes additional, mysterious restrictions on model numbers, and legend says the last copy of the MONAD documentation was eaten by a tanuki. You'll need to figure out what MONAD does some other way. To enable as many submarine features as possible, find the largest valid fourteen-digit model number that contains no 0 digits. What is the largest model number accepted by MONAD?	25
--- Day 14: Restroom Redoubt --- One of The Historians needs to use the bathroom; fortunately, you know there's a bathroom near an unvisited location on their list, and so you're all quickly teleported directly to the lobby of Easter Bunny Headquarters. Unfortunately, EBHQ seems to have "improved" bathroom security again after your last visit. The area outside the bathroom is swarming with robots! To get The Historian safely to the bathroom, you'll need a way to predict where the robots will be in the future. Fortunately, they all seem to be moving on the tile floor in predictable straight lines. You make a list (your puzzle input) of all of the robots' current positions (p) and velocities (v), one robot per line. For example: p=0,4 v=3,-3 p=6,3 v=-1,-3 p=10,3 v=-1,2 p=2,0 v=2,-1 p=0,0 v=1,3 p=3,0 v=-2,-2 p=7,6 v=-1,-3 p=3,0 v=-1,-2 p=9,3 v=2,3 p=7,3 v=-1,2 p=2,4 v=2,-3 p=9,5 v=-3,-3 Each robot's position is given as p=x,y where x represents the number of tiles the robot is from the left wall and y represents the number of tiles from the top wall (when viewed from above). So, a position of p=0,0 means the robot is all the way in the top-left corner. Each robot's velocity is given as v=x,y where x and y are given in tiles per second. Positive x means the robot is moving to the right, and positive y means the robot is moving down. So, a velocity of v=1,-2 means that each second, the robot moves 1 tile to the right and 2 tiles up. The robots outside the actual bathroom are in a space which is 101 tiles wide and 103 tiles tall (when viewed from above). However, in this example, the robots are in a space which is only 11 tiles wide and 7 tiles tall. The robots are good at navigating over/under each other (due to a combination of springs, extendable legs, and quadcopters), so they can share the same tile and don't interact with each other. Visually, the number of robots on each tile in this example looks like this: 1.12....... ........... ........... ......11.11 1.1........ .........1. .......1... These robots have a unique feature for maximum bathroom security: they can teleport. When a robot would run into an edge of the space they're in, they instead teleport to the other side, effectively wrapping around the edges. Here is what robot p=2,4 v=2,-3 does for the first few seconds: Initial state: ........... ........... ........... ........... ..1........ ........... ........... After 1 second: ........... ....1...... ........... ........... ........... ........... ........... After 2 seconds: ........... ........... ........... ........... ........... ......1.... ........... After 3 seconds: ........... ........... ........1.. ........... ........... ........... ........... After 4 seconds: ........... ........... ........... ........... ........... ........... ..........1 After 5 seconds: ........... ........... ........... .1......... ........... ........... ........... The Historian can't wait much longer, so you don't have to simulate the robots for very long. Where will the robots be after 100 seconds? In the above example, the number of robots on each tile after 100 seconds has elapsed looks like this: ......2..1. ........... 1.......... .11........ .....1..... ...12...... .1....1.... To determine the safest area, count the number of robots in each quadrant after 100 seconds. Robots that are exactly in the middle (horizontally or vertically) don't count as being in any quadrant, so the only relevant robots are: ..... 2..1. ..... ..... 1.... ..... ..... ..... ...12 ..... .1... 1.... In this example, the quadrants contain 1, 3, 4, and 1 robot. Multiplying these together gives a total safety factor of 12. Predict the motion of the robots in your list within a space which is 101 tiles wide and 103 tiles tall. What will the safety factor be after exactly 100 seconds have elapsed? Your puzzle answer was 221655456. The first half of this puzzle is complete! It provides one gold star: * --- Part Two --- During the bathroom break, someone notices that these robots seem awfully similar to ones built and used at the North Pole. If they're the same type of robots, they should have a hard-coded Easter egg: very rarely, most of the robots should arrange themselves into a picture of a Christmas tree. What is the fewest number of seconds that must elapse for the robots to display the Easter egg?	26
--- Day 3: Spiral Memory --- You come across an experimental new kind of memory stored on an infinite two-dimensional grid. Each square on the grid is allocated in a spiral pattern starting at a location marked 1 and then counting up while spiraling outward. For example, the first few squares are allocated like this: 17 16 15 14 13 18 5 4 3 12 19 6 1 2 11 20 7 8 9 10 21 22 23---> ... While this is very space-efficient (no squares are skipped), requested data must be carried back to square 1 (the location of the only access port for this memory system) by programs that can only move up, down, left, or right. They always take the shortest path: the Manhattan Distance between the location of the data and square 1. For example: Data from square 1 is carried 0 steps, since it's at the access port. Data from square 12 is carried 3 steps, such as: down, left, left. Data from square 23 is carried only 2 steps: up twice. Data from square 1024 must be carried 31 steps. How many steps are required to carry the data from the square identified in your puzzle input all the way to the access port?	27
--- Day 1: Report Repair --- After saving Christmas five years in a row, you've decided to take a vacation at a nice resort on a tropical island. Surely, Christmas will go on without you. The tropical island has its own currency and is entirely cash-only. The gold coins used there have a little picture of a starfish; the locals just call them stars. None of the currency exchanges seem to have heard of them, but somehow, you'll need to find fifty of these coins by the time you arrive so you can pay the deposit on your room. To save your vacation, you need to get all fifty stars by December 25th. Collect stars by solving puzzles. Two puzzles will be made available on each day in the Advent calendar; the second puzzle is unlocked when you complete the first. Each puzzle grants one star. Good luck! Before you leave, the Elves in accounting just need you to fix your expense report (your puzzle input); apparently, something isn't quite adding up. Specifically, they need you to find the two entries that sum to 2020 and then multiply those two numbers together. For example, suppose your expense report contained the following: 1721 979 366 299 675 1456 In this list, the two entries that sum to 2020 are 1721 and 299. Multiplying them together produces 1721 * 299 = 514579, so the correct answer is 514579. Of course, your expense report is much larger. Find the two entries that sum to 2020; what do you get if you multiply them together? Your puzzle answer was 381699. --- Part Two --- The Elves in accounting are thankful for your help; one of them even offers you a starfish coin they had left over from a past vacation. They offer you a second one if you can find three numbers in your expense report that meet the same criteria. Using the above example again, the three entries that sum to 2020 are 979, 366, and 675. Multiplying them together produces the answer, 241861950. In your expense report, what is the product of the three entries that sum to 2020?	28
--- Day 20: Particle Swarm --- Suddenly, the GPU contacts you, asking for help. Someone has asked it to simulate too many particles, and it won't be able to finish them all in time to render the next frame at this rate. It transmits to you a buffer (your puzzle input) listing each particle in order (starting with particle 0, then particle 1, particle 2, and so on). For each particle, it provides the X, Y, and Z coordinates for the particle's position (p), velocity (v), and acceleration (a), each in the format <X,Y,Z>. Each tick, all particles are updated simultaneously. A particle's properties are updated in the following order: Increase the X velocity by the X acceleration. Increase the Y velocity by the Y acceleration. Increase the Z velocity by the Z acceleration. Increase the X position by the X velocity. Increase the Y position by the Y velocity. Increase the Z position by the Z velocity. Because of seemingly tenuous rationale involving z-buffering, the GPU would like to know which particle will stay closest to position <0,0,0> in the long term. Measure this using the Manhattan distance, which in this situation is simply the sum of the absolute values of a particle's X, Y, and Z position. For example, suppose you are only given two particles, both of which stay entirely on the X-axis (for simplicity). Drawing the current states of particles 0 and 1 (in that order) with an adjacent a number line and diagram of current X positions (marked in parentheses), the following would take place: p=< 3,0,0>, v=< 2,0,0>, a=<-1,0,0> -4 -3 -2 -1 0 1 2 3 4 p=< 4,0,0>, v=< 0,0,0>, a=<-2,0,0> (0)(1) p=< 4,0,0>, v=< 1,0,0>, a=<-1,0,0> -4 -3 -2 -1 0 1 2 3 4 p=< 2,0,0>, v=<-2,0,0>, a=<-2,0,0> (1) (0) p=< 4,0,0>, v=< 0,0,0>, a=<-1,0,0> -4 -3 -2 -1 0 1 2 3 4 p=<-2,0,0>, v=<-4,0,0>, a=<-2,0,0> (1) (0) p=< 3,0,0>, v=<-1,0,0>, a=<-1,0,0> -4 -3 -2 -1 0 1 2 3 4 p=<-8,0,0>, v=<-6,0,0>, a=<-2,0,0> (0) At this point, particle 1 will never be closer to <0,0,0> than particle 0, and so, in the long run, particle 0 will stay closest. Which particle will stay closest to position <0,0,0> in the long term?	29
--- Day 7: Internet Protocol Version 7 --- While snooping around the local network of EBHQ, you compile a list of IP addresses (they're IPv7, of course; IPv6 is much too limited). You'd like to figure out which IPs support TLS (transport-layer snooping). An IP supports TLS if it has an Autonomous Bridge Bypass Annotation, or ABBA. An ABBA is any four-character sequence which consists of a pair of two different characters followed by the reverse of that pair, such as xyyx or abba. However, the IP also must not have an ABBA within any hypernet sequences, which are contained by square brackets. For example: abba[mnop]qrst supports TLS (abba outside square brackets). abcd[bddb]xyyx does not support TLS (bddb is within square brackets, even though xyyx is outside square brackets). aaaa[qwer]tyui does not support TLS (aaaa is invalid; the interior characters must be different). ioxxoj[asdfgh]zxcvbn supports TLS (oxxo is outside square brackets, even though it's within a larger string). How many IPs in your puzzle input support TLS?	30
--- Day 7: Camel Cards --- Your all-expenses-paid trip turns out to be a one-way, five-minute ride in an airship. (At least it's a cool airship!) It drops you off at the edge of a vast desert and descends back to Island Island. "Did you bring the parts?" You turn around to see an Elf completely covered in white clothing, wearing goggles, and riding a large camel. "Did you bring the parts?" she asks again, louder this time. You aren't sure what parts she's looking for; you're here to figure out why the sand stopped. "The parts! For the sand, yes! Come with me; I will show you." She beckons you onto the camel. After riding a bit across the sands of Desert Island, you can see what look like very large rocks covering half of the horizon. The Elf explains that the rocks are all along the part of Desert Island that is directly above Island Island, making it hard to even get there. Normally, they use big machines to move the rocks and filter the sand, but the machines have broken down because Desert Island recently stopped receiving the parts they need to fix the machines. You've already assumed it'll be your job to figure out why the parts stopped when she asks if you can help. You agree automatically. Because the journey will take a few days, she offers to teach you the game of Camel Cards. Camel Cards is sort of similar to poker except it's designed to be easier to play while riding a camel. In Camel Cards, you get a list of hands, and your goal is to order them based on the strength of each hand. A hand consists of five cards labeled one of A, K, Q, J, T, 9, 8, 7, 6, 5, 4, 3, or 2. The relative strength of each card follows this order, where A is the highest and 2 is the lowest. Every hand is exactly one type. From strongest to weakest, they are: Five of a kind, where all five cards have the same label: AAAAA Four of a kind, where four cards have the same label and one card has a different label: AA8AA Full house, where three cards have the same label, and the remaining two cards share a different label: 23332 Three of a kind, where three cards have the same label, and the remaining two cards are each different from any other card in the hand: TTT98 Two pair, where two cards share one label, two other cards share a second label, and the remaining card has a third label: 23432 One pair, where two cards share one label, and the other three cards have a different label from the pair and each other: A23A4 High card, where all cards' labels are distinct: 23456 Hands are primarily ordered based on type; for example, every full house is stronger than any three of a kind. If two hands have the same type, a second ordering rule takes effect. Start by comparing the first card in each hand. If these cards are different, the hand with the stronger first card is considered stronger. If the first card in each hand have the same label, however, then move on to considering the second card in each hand. If they differ, the hand with the higher second card wins; otherwise, continue with the third card in each hand, then the fourth, then the fifth. So, 33332 and 2AAAA are both four of a kind hands, but 33332 is stronger because its first card is stronger. Similarly, 77888 and 77788 are both a full house, but 77888 is stronger because its third card is stronger (and both hands have the same first and second card). To play Camel Cards, you are given a list of hands and their corresponding bid (your puzzle input). For example: 32T3K 765 T55J5 684 KK677 28 KTJJT 220 QQQJA 483 This example shows five hands; each hand is followed by its bid amount. Each hand wins an amount equal to its bid multiplied by its rank, where the weakest hand gets rank 1, the second-weakest hand gets rank 2, and so on up to the strongest hand. Because there are five hands in this example, the strongest hand will have rank 5 and its bid will be multiplied by 5. So, the first step is to put the hands in order of strength: 32T3K is the only one pair and the other hands are all a stronger type, so it gets rank 1. KK677 and KTJJT are both two pair. Their first cards both have the same label, but the second card of KK677 is stronger (K vs T), so KTJJT gets rank 2 and KK677 gets rank 3. T55J5 and QQQJA are both three of a kind. QQQJA has a stronger first card, so it gets rank 5 and T55J5 gets rank 4. Now, you can determine the total winnings of this set of hands by adding up the result of multiplying each hand's bid with its rank (765 * 1 + 220 * 2 + 28 * 3 + 684 * 4 + 483 * 5). So the total winnings in this example are 6440. Find the rank of every hand in your set. What are the total winnings?	31
--- Day 13: A Maze of Twisty Little Cubicles --- You arrive at the first floor of this new building to discover a much less welcoming environment than the shiny atrium of the last one. Instead, you are in a maze of twisty little cubicles, all alike. Every location in this area is addressed by a pair of non-negative integers (x,y). Each such coordinate is either a wall or an open space. You can't move diagonally. The cube maze starts at 0,0 and seems to extend infinitely toward positive x and y; negative values are invalid, as they represent a location outside the building. You are in a small waiting area at 1,1. While it seems chaotic, a nearby morale-boosting poster explains, the layout is actually quite logical. You can determine whether a given x,y coordinate will be a wall or an open space using a simple system: Find xx + 3x + 2xy + y + y*y. Add the office designer's favorite number (your puzzle input). Find the binary representation of that sum; count the number of bits that are 1. If the number of bits that are 1 is even, it's an open space. If the number of bits that are 1 is odd, it's a wall. For example, if the office designer's favorite number were 10, drawing walls as # and open spaces as ., the corner of the building containing 0,0 would look like this: 0123456789 0 .#.####.## 1 ..#..#...# 2 #....##... 3 ###.#.###. 4 .##..#..#. 5 ..##....#. 6 #...##.### Now, suppose you wanted to reach 7,4. The shortest route you could take is marked as O: 0123456789 0 .#.####.## 1 .O#..#...# 2 #OOO.##... 3 ###O#.###. 4 .##OO#OO#. 5 ..##OOO.#. 6 #...##.### Thus, reaching 7,4 would take a minimum of 11 steps (starting from your current location, 1,1). What is the fewest number of steps required for you to reach 31,39? Your puzzle answer was 82. --- Part Two --- How many locations (distinct x,y coordinates, including your starting location) can you reach in at most 50 steps?	32
--- Day 11: Cosmic Expansion --- You continue following signs for "Hot Springs" and eventually come across an observatory. The Elf within turns out to be a researcher studying cosmic expansion using the giant telescope here. He doesn't know anything about the missing machine parts; he's only visiting for this research project. However, he confirms that the hot springs are the next-closest area likely to have people; he'll even take you straight there once he's done with today's observation analysis. Maybe you can help him with the analysis to speed things up? The researcher has collected a bunch of data and compiled the data into a single giant image (your puzzle input). The image includes empty space (.) and galaxies (#). For example: ...#...... .......#.. #......... .......... ......#... .#........ .........# .......... .......#.. #...#..... The researcher is trying to figure out the sum of the lengths of the shortest path between every pair of galaxies. However, there's a catch: the universe expanded in the time it took the light from those galaxies to reach the observatory. Due to something involving gravitational effects, only some space expands. In fact, the result is that any rows or columns that contain no galaxies should all actually be twice as big. In the above example, three columns and two rows contain no galaxies: v v v ...#...... .......#.. #......... >..........< ......#... .#........ .........# >..........< .......#.. #...#..... ^ ^ ^ These rows and columns need to be twice as big; the result of cosmic expansion therefore looks like this: ....#........ .........#... #............ ............. ............. ........#.... .#........... ............# ............. ............. .........#... #....#....... Equipped with this expanded universe, the shortest path between every pair of galaxies can be found. It can help to assign every galaxy a unique number: ....1........ .........2... 3............ ............. ............. ........4.... .5........... ............6 ............. ............. .........7... 8....9....... In these 9 galaxies, there are 36 pairs. Only count each pair once; order within the pair doesn't matter. For each pair, find any shortest path between the two galaxies using only steps that move up, down, left, or right exactly one . or # at a time. (The shortest path between two galaxies is allowed to pass through another galaxy.) For example, here is one of the shortest paths between galaxies 5 and 9: ....1........ .........2... 3............ ............. ............. ........4.... .5........... .##.........6 ..##......... ...##........ ....##...7... 8....9....... This path has length 9 because it takes a minimum of nine steps to get from galaxy 5 to galaxy 9 (the eight locations marked # plus the step onto galaxy 9 itself). Here are some other example shortest path lengths: Between galaxy 1 and galaxy 7: 15 Between galaxy 3 and galaxy 6: 17 Between galaxy 8 and galaxy 9: 5 In this example, after expanding the universe, the sum of the shortest path between all 36 pairs of galaxies is 374. Expand the universe, then find the length of the shortest path between every pair of galaxies. What is the sum of these lengths?	33
--- Day 6: Guard Gallivant --- The Historians use their fancy device again, this time to whisk you all away to the North Pole prototype suit manufacturing lab... in the year 1518! It turns out that having direct access to history is very convenient for a group of historians. You still have to be careful of time paradoxes, and so it will be important to avoid anyone from 1518 while The Historians search for the Chief. Unfortunately, a single guard is patrolling this part of the lab. Maybe you can work out where the guard will go ahead of time so that The Historians can search safely? You start by making a map (your puzzle input) of the situation. For example: ....#..... .........# .......... ..#....... .......#.. .......... .#..^..... ........#. #......... ......#... The map shows the current position of the guard with ^ (to indicate the guard is currently facing up from the perspective of the map). Any obstructions - crates, desks, alchemical reactors, etc. - are shown as #. Lab guards in 1518 follow a very strict patrol protocol which involves repeatedly following these steps: If there is something directly in front of you, turn right 90 degrees. Otherwise, take a step forward. Following the above protocol, the guard moves up several times until she reaches an obstacle (in this case, a pile of failed suit prototypes): ....#..... ....^....# .......... ..#....... .......#.. .......... .#........ ........#. #......... ......#... Because there is now an obstacle in front of the guard, she turns right before continuing straight in her new facing direction: ....#..... ........># .......... ..#....... .......#.. .......... .#........ ........#. #......... ......#... Reaching another obstacle (a spool of several very long polymers), she turns right again and continues downward: ....#..... .........# .......... ..#....... .......#.. .......... .#......v. ........#. #......... ......#... This process continues for a while, but the guard eventually leaves the mapped area (after walking past a tank of universal solvent): ....#..... .........# .......... ..#....... .......#.. .......... .#........ ........#. #......... ......#v.. By predicting the guard's route, you can determine which specific positions in the lab will be in the patrol path. Including the guard's starting position, the positions visited by the guard before leaving the area are marked with an X: ....#..... ....XXXXX# ....X...X. ..#.X...X. ..XXXXX#X. ..X.X.X.X. .#XXXXXXX. .XXXXXXX#. #XXXXXXX.. ......#X.. In this example, the guard will visit 41 distinct positions on your map. Predict the path of the guard. How many distinct positions will the guard visit before leaving the mapped area? Your puzzle answer was 4988. The first half of this puzzle is complete! It provides one gold star: * --- Part Two --- While The Historians begin working around the guard's patrol route, you borrow their fancy device and step outside the lab. From the safety of a supply closet, you time travel through the last few months and record the nightly status of the lab's guard post on the walls of the closet. Returning after what seems like only a few seconds to The Historians, they explain that the guard's patrol area is simply too large for them to safely search the lab without getting caught. Fortunately, they are pretty sure that adding a single new obstruction won't cause a time paradox. They'd like to place the new obstruction in such a way that the guard will get stuck in a loop, making the rest of the lab safe to search. To have the lowest chance of creating a time paradox, The Historians would like to know all of the possible positions for such an obstruction. The new obstruction can't be placed at the guard's starting position - the guard is there right now and would notice. In the above example, there are only 6 different positions where a new obstruction would cause the guard to get stuck in a loop. The diagrams of these six situations use O to mark the new obstruction, \| to show a position where the guard moves up/down, - to show a position where the guard moves left/right, and + to show a position where the guard moves both up/down and left/right. Option one, put a printing press next to the guard's starting position: ....#..... ....+---+# ....\|...\|. ..#.\|...\|. ....\|..#\|. ....\|...\|. .#.O^---+. ........#. #......... ......#... Option two, put a stack of failed suit prototypes in the bottom right quadrant of the mapped area: ....#..... ....+---+# ....\|...\|. ..#.\|...\|. ..+-+-+#\|. ..\|.\|.\|.\|. .#+-^-+-+. ......O.#. #......... ......#... Option three, put a crate of chimney-squeeze prototype fabric next to the standing desk in the bottom right quadrant: ....#..... ....+---+# ....\|...\|. ..#.\|...\|. ..+-+-+#\|. ..\|.\|.\|.\|. .#+-^-+-+. .+----+O#. #+----+... ......#... Option four, put an alchemical retroencabulator near the bottom left corner: ....#..... ....+---+# ....\|...\|. ..#.\|...\|. ..+-+-+#\|. ..\|.\|.\|.\|. .#+-^-+-+. ..\|...\|.#. #O+---+... ......#... Option five, put the alchemical retroencabulator a bit to the right instead: ....#..... ....+---+# ....\|...\|. ..#.\|...\|. ..+-+-+#\|. ..\|.\|.\|.\|. .#+-^-+-+. ....\|.\|.#. #..O+-+... ......#... Option six, put a tank of sovereign glue right next to the tank of universal solvent: ....#..... ....+---+# ....\|...\|. ..#.\|...\|. ..+-+-+#\|. ..\|.\|.\|.\|. .#+-^-+-+. .+----++#. #+----++.. ......#O.. It doesn't really matter what you choose to use as an obstacle so long as you and The Historians can put it into position without the guard noticing. The important thing is having enough options that you can find one that minimizes time paradoxes, and in this example, there are 6 different positions you could choose. You need to get the guard stuck in a loop by adding a single new obstruction. How many different positions could you choose for this obstruction?	34
--- Day 2: Red-Nosed Reports --- Fortunately, the first location The Historians want to search isn't a long walk from the Chief Historian's office. While the Red-Nosed Reindeer nuclear fusion/fission plant appears to contain no sign of the Chief Historian, the engineers there run up to you as soon as they see you. Apparently, they still talk about the time Rudolph was saved through molecular synthesis from a single electron. They're quick to add that - since you're already here - they'd really appreciate your help analyzing some unusual data from the Red-Nosed reactor. You turn to check if The Historians are waiting for you, but they seem to have already divided into groups that are currently searching every corner of the facility. You offer to help with the unusual data. The unusual data (your puzzle input) consists of many reports, one report per line. Each report is a list of numbers called levels that are separated by spaces. For example: 7 6 4 2 1 1 2 7 8 9 9 7 6 2 1 1 3 2 4 5 8 6 4 4 1 1 3 6 7 9 This example data contains six reports each containing five levels. The engineers are trying to figure out which reports are safe. The Red-Nosed reactor safety systems can only tolerate levels that are either gradually increasing or gradually decreasing. So, a report only counts as safe if both of the following are true: The levels are either all increasing or all decreasing. Any two adjacent levels differ by at least one and at most three. In the example above, the reports can be found safe or unsafe by checking those rules: 7 6 4 2 1: Safe because the levels are all decreasing by 1 or 2. 1 2 7 8 9: Unsafe because 2 7 is an increase of 5. 9 7 6 2 1: Unsafe because 6 2 is a decrease of 4. 1 3 2 4 5: Unsafe because 1 3 is increasing but 3 2 is decreasing. 8 6 4 4 1: Unsafe because 4 4 is neither an increase or a decrease. 1 3 6 7 9: Safe because the levels are all increasing by 1, 2, or 3. So, in this example, 2 reports are safe. Analyze the unusual data from the engineers. How many reports are safe?	35
--- Day 19: Go With The Flow --- With the Elves well on their way constructing the North Pole base, you turn your attention back to understanding the inner workings of programming the device. You can't help but notice that the device's opcodes don't contain any flow control like jump instructions. The device's manual goes on to explain: "In programs where flow control is required, the instruction pointer can be bound to a register so that it can be manipulated directly. This way, setr/seti can function as absolute jumps, addr/addi can function as relative jumps, and other opcodes can cause truly fascinating effects." This mechanism is achieved through a declaration like #ip 1, which would modify register 1 so that accesses to it let the program indirectly access the instruction pointer itself. To compensate for this kind of binding, there are now six registers (numbered 0 through 5); the five not bound to the instruction pointer behave as normal. Otherwise, the same rules apply as the last time you worked with this device. When the instruction pointer is bound to a register, its value is written to that register just before each instruction is executed, and the value of that register is written back to the instruction pointer immediately after each instruction finishes execution. Afterward, move to the next instruction by adding one to the instruction pointer, even if the value in the instruction pointer was just updated by an instruction. (Because of this, instructions must effectively set the instruction pointer to the instruction before the one they want executed next.) The instruction pointer is 0 during the first instruction, 1 during the second, and so on. If the instruction pointer ever causes the device to attempt to load an instruction outside the instructions defined in the program, the program instead immediately halts. The instruction pointer starts at 0. It turns out that this new information is already proving useful: the CPU in the device is not very powerful, and a background process is occupying most of its time. You dump the background process' declarations and instructions to a file (your puzzle input), making sure to use the names of the opcodes rather than the numbers. For example, suppose you have the following program: #ip 0 seti 5 0 1 seti 6 0 2 addi 0 1 0 addr 1 2 3 setr 1 0 0 seti 8 0 4 seti 9 0 5 When executed, the following instructions are executed. Each line contains the value of the instruction pointer at the time the instruction started, the values of the six registers before executing the instructions (in square brackets), the instruction itself, and the values of the six registers after executing the instruction (also in square brackets). ip=0 [0, 0, 0, 0, 0, 0] seti 5 0 1 [0, 5, 0, 0, 0, 0] ip=1 [1, 5, 0, 0, 0, 0] seti 6 0 2 [1, 5, 6, 0, 0, 0] ip=2 [2, 5, 6, 0, 0, 0] addi 0 1 0 [3, 5, 6, 0, 0, 0] ip=4 [4, 5, 6, 0, 0, 0] setr 1 0 0 [5, 5, 6, 0, 0, 0] ip=6 [6, 5, 6, 0, 0, 0] seti 9 0 5 [6, 5, 6, 0, 0, 9] In detail, when running this program, the following events occur: The first line (#ip 0) indicates that the instruction pointer should be bound to register 0 in this program. This is not an instruction, and so the value of the instruction pointer does not change during the processing of this line. The instruction pointer contains 0, and so the first instruction is executed (seti 5 0 1). It updates register 0 to the current instruction pointer value (0), sets register 1 to 5, sets the instruction pointer to the value of register 0 (which has no effect, as the instruction did not modify register 0), and then adds one to the instruction pointer. The instruction pointer contains 1, and so the second instruction, seti 6 0 2, is executed. This is very similar to the instruction before it: 6 is stored in register 2, and the instruction pointer is left with the value 2. The instruction pointer is 2, which points at the instruction addi 0 1 0. This is like a relative jump: the value of the instruction pointer, 2, is loaded into register 0. Then, addi finds the result of adding the value in register 0 and the value 1, storing the result, 3, back in register 0. Register 0 is then copied back to the instruction pointer, which will cause it to end up 1 larger than it would have otherwise and skip the next instruction (addr 1 2 3) entirely. Finally, 1 is added to the instruction pointer. The instruction pointer is 4, so the instruction setr 1 0 0 is run. This is like an absolute jump: it copies the value contained in register 1, 5, into register 0, which causes it to end up in the instruction pointer. The instruction pointer is then incremented, leaving it at 6. The instruction pointer is 6, so the instruction seti 9 0 5 stores 9 into register 5. The instruction pointer is incremented, causing it to point outside the program, and so the program ends. What value is left in register 0 when the background process halts? Your puzzle answer was 1430. --- Part Two --- A new background process immediately spins up in its place. It appears identical, but on closer inspection, you notice that this time, register 0 started with the value 1. What value is left in register 0 when this new background process halts?	36
--- Day 21: RPG Simulator 20XX --- Little Henry Case got a new video game for Christmas. It's an RPG, and he's stuck on a boss. He needs to know what equipment to buy at the shop. He hands you the controller. In this game, the player (you) and the enemy (the boss) take turns attacking. The player always goes first. Each attack reduces the opponent's hit points by at least 1. The first character at or below 0 hit points loses. Damage dealt by an attacker each turn is equal to the attacker's damage score minus the defender's armor score. An attacker always does at least 1 damage. So, if the attacker has a damage score of 8, and the defender has an armor score of 3, the defender loses 5 hit points. If the defender had an armor score of 300, the defender would still lose 1 hit point. Your damage score and armor score both start at zero. They can be increased by buying items in exchange for gold. You start with no items and have as much gold as you need. Your total damage or armor is equal to the sum of those stats from all of your items. You have 100 hit points. Here is what the item shop is selling: Weapons: Cost Damage Armor Dagger 8 4 0 Shortsword 10 5 0 Warhammer 25 6 0 Longsword 40 7 0 Greataxe 74 8 0 Armor: Cost Damage Armor Leather 13 0 1 Chainmail 31 0 2 Splintmail 53 0 3 Bandedmail 75 0 4 Platemail 102 0 5 Rings: Cost Damage Armor Damage +1 25 1 0 Damage +2 50 2 0 Damage +3 100 3 0 Defense +1 20 0 1 Defense +2 40 0 2 Defense +3 80 0 3 You must buy exactly one weapon; no dual-wielding. Armor is optional, but you can't use more than one. You can buy 0-2 rings (at most one for each hand). You must use any items you buy. The shop only has one of each item, so you can't buy, for example, two rings of Damage +3. For example, suppose you have 8 hit points, 5 damage, and 5 armor, and that the boss has 12 hit points, 7 damage, and 2 armor: The player deals 5-2 = 3 damage; the boss goes down to 9 hit points. The boss deals 7-5 = 2 damage; the player goes down to 6 hit points. The player deals 5-2 = 3 damage; the boss goes down to 6 hit points. The boss deals 7-5 = 2 damage; the player goes down to 4 hit points. The player deals 5-2 = 3 damage; the boss goes down to 3 hit points. The boss deals 7-5 = 2 damage; the player goes down to 2 hit points. The player deals 5-2 = 3 damage; the boss goes down to 0 hit points. In this scenario, the player wins! (Barely.) You have 100 hit points. The boss's actual stats are in your puzzle input. What is the least amount of gold you can spend and still win the fight?	37
--- Day 14: One-Time Pad --- In order to communicate securely with Santa while you're on this mission, you've been using a one-time pad that you generate using a pre-agreed algorithm. Unfortunately, you've run out of keys in your one-time pad, and so you need to generate some more. To generate keys, you first get a stream of random data by taking the MD5 of a pre-arranged salt (your puzzle input) and an increasing integer index (starting with 0, and represented in decimal); the resulting MD5 hash should be represented as a string of lowercase hexadecimal digits. However, not all of these MD5 hashes are keys, and you need 64 new keys for your one-time pad. A hash is a key only if: It contains three of the same character in a row, like 777. Only consider the first such triplet in a hash. One of the next 1000 hashes in the stream contains that same character five times in a row, like 77777. Considering future hashes for five-of-a-kind sequences does not cause those hashes to be skipped; instead, regardless of whether the current hash is a key, always resume testing for keys starting with the very next hash. For example, if the pre-arranged salt is abc: The first index which produces a triple is 18, because the MD5 hash of abc18 contains ...cc38887a5.... However, index 18 does not count as a key for your one-time pad, because none of the next thousand hashes (index 19 through index 1018) contain 88888. The next index which produces a triple is 39; the hash of abc39 contains eee. It is also the first key: one of the next thousand hashes (the one at index 816) contains eeeee. None of the next six triples are keys, but the one after that, at index 92, is: it contains 999 and index 200 contains 99999. Eventually, index 22728 meets all of the criteria to generate the 64th key. So, using our example salt of abc, index 22728 produces the 64th key. Given the actual salt in your puzzle input, what index produces your 64th one-time pad key? Your puzzle answer was 16106. --- Part Two --- Of course, in order to make this process even more secure, you've also implemented key stretching. Key stretching forces attackers to spend more time generating hashes. Unfortunately, it forces everyone else to spend more time, too. To implement key stretching, whenever you generate a hash, before you use it, you first find the MD5 hash of that hash, then the MD5 hash of that hash, and so on, a total of 2016 additional hashings. Always use lowercase hexadecimal representations of hashes. For example, to find the stretched hash for index 0 and salt abc: Find the MD5 hash of abc0: 577571be4de9dcce85a041ba0410f29f. Then, find the MD5 hash of that hash: eec80a0c92dc8a0777c619d9bb51e910. Then, find the MD5 hash of that hash: 16062ce768787384c81fe17a7a60c7e3. ...repeat many times... Then, find the MD5 hash of that hash: a107ff634856bb300138cac6568c0f24. So, the stretched hash for index 0 in this situation is a107ff.... In the end, you find the original hash (one use of MD5), then find the hash-of-the-previous-hash 2016 times, for a total of 2017 uses of MD5. The rest of the process remains the same, but now the keys are entirely different. Again for salt abc: The first triple (222, at index 5) has no matching 22222 in the next thousand hashes. The second triple (eee, at index 10) hash a matching eeeee at index 89, and so it is the first key. Eventually, index 22551 produces the 64th key (triple fff with matching fffff at index 22859. Given the actual salt in your puzzle input and using 2016 extra MD5 calls of key stretching, what index now produces your 64th one-time pad key?	38
--- Day 5: Sunny with a Chance of Asteroids --- You're starting to sweat as the ship makes its way toward Mercury. The Elves suggest that you get the air conditioner working by upgrading your ship computer to support the Thermal Environment Supervision Terminal. The Thermal Environment Supervision Terminal (TEST) starts by running a diagnostic program (your puzzle input). The TEST diagnostic program will run on your existing Intcode computer after a few modifications: First, you'll need to add two new instructions: Opcode 3 takes a single integer as input and saves it to the position given by its only parameter. For example, the instruction 3,50 would take an input value and store it at address 50. Opcode 4 outputs the value of its only parameter. For example, the instruction 4,50 would output the value at address 50. Programs that use these instructions will come with documentation that explains what should be connected to the input and output. The program 3,0,4,0,99 outputs whatever it gets as input, then halts. Second, you'll need to add support for parameter modes: Each parameter of an instruction is handled based on its parameter mode. Right now, your ship computer already understands parameter mode 0, position mode, which causes the parameter to be interpreted as a position - if the parameter is 50, its value is the value stored at address 50 in memory. Until now, all parameters have been in position mode. Now, your ship computer will also need to handle parameters in mode 1, immediate mode. In immediate mode, a parameter is interpreted as a value - if the parameter is 50, its value is simply 50. Parameter modes are stored in the same value as the instruction's opcode. The opcode is a two-digit number based only on the ones and tens digit of the value, that is, the opcode is the rightmost two digits of the first value in an instruction. Parameter modes are single digits, one per parameter, read right-to-left from the opcode: the first parameter's mode is in the hundreds digit, the second parameter's mode is in the thousands digit, the third parameter's mode is in the ten-thousands digit, and so on. Any missing modes are 0. For example, consider the program 1002,4,3,4,33. The first instruction, 1002,4,3,4, is a multiply instruction - the rightmost two digits of the first value, 02, indicate opcode 2, multiplication. Then, going right to left, the parameter modes are 0 (hundreds digit), 1 (thousands digit), and 0 (ten-thousands digit, not present and therefore zero): ABCDE 1002 DE - two-digit opcode, 02 == opcode 2 C - mode of 1st parameter, 0 == position mode B - mode of 2nd parameter, 1 == immediate mode A - mode of 3rd parameter, 0 == position mode, omitted due to being a leading zero This instruction multiplies its first two parameters. The first parameter, 4 in position mode, works like it did before - its value is the value stored at address 4 (33). The second parameter, 3 in immediate mode, simply has value 3. The result of this operation, 33 * 3 = 99, is written according to the third parameter, 4 in position mode, which also works like it did before - 99 is written to address 4. Parameters that an instruction writes to will never be in immediate mode. Finally, some notes: It is important to remember that the instruction pointer should increase by the number of values in the instruction after the instruction finishes. Because of the new instructions, this amount is no longer always 4. Integers can be negative: 1101,100,-1,4,0 is a valid program (find 100 + -1, store the result in position 4). The TEST diagnostic program will start by requesting from the user the ID of the system to test by running an input instruction - provide it 1, the ID for the ship's air conditioner unit. It will then perform a series of diagnostic tests confirming that various parts of the Intcode computer, like parameter modes, function correctly. For each test, it will run an output instruction indicating how far the result of the test was from the expected value, where 0 means the test was successful. Non-zero outputs mean that a function is not working correctly; check the instructions that were run before the output instruction to see which one failed. Finally, the program will output a diagnostic code and immediately halt. This final output isn't an error; an output followed immediately by a halt means the program finished. If all outputs were zero except the diagnostic code, the diagnostic program ran successfully. After providing 1 to the only input instruction and passing all the tests, what diagnostic code does the program produce? Your puzzle answer was 14522484. --- Part Two --- The air conditioner comes online! Its cold air feels good for a while, but then the TEST alarms start to go off. Since the air conditioner can't vent its heat anywhere but back into the spacecraft, it's actually making the air inside the ship warmer. Instead, you'll need to use the TEST to extend the thermal radiators. Fortunately, the diagnostic program (your puzzle input) is already equipped for this. Unfortunately, your Intcode computer is not. Your computer is only missing a few opcodes: Opcode 5 is jump-if-true: if the first parameter is non-zero, it sets the instruction pointer to the value from the second parameter. Otherwise, it does nothing. Opcode 6 is jump-if-false: if the first parameter is zero, it sets the instruction pointer to the value from the second parameter. Otherwise, it does nothing. Opcode 7 is less than: if the first parameter is less than the second parameter, it stores 1 in the position given by the third parameter. Otherwise, it stores 0. Opcode 8 is equals: if the first parameter is equal to the second parameter, it stores 1 in the position given by the third parameter. Otherwise, it stores 0. Like all instructions, these instructions need to support parameter modes as described above. Normally, after an instruction is finished, the instruction pointer increases by the number of values in that instruction. However, if the instruction modifies the instruction pointer, that value is used and the instruction pointer is not automatically increased. For example, here are several programs that take one input, compare it to the value 8, and then produce one output: 3,9,8,9,10,9,4,9,99,-1,8 - Using position mode, consider whether the input is equal to 8; output 1 (if it is) or 0 (if it is not). 3,9,7,9,10,9,4,9,99,-1,8 - Using position mode, consider whether the input is less than 8; output 1 (if it is) or 0 (if it is not). 3,3,1108,-1,8,3,4,3,99 - Using immediate mode, consider whether the input is equal to 8; output 1 (if it is) or 0 (if it is not). 3,3,1107,-1,8,3,4,3,99 - Using immediate mode, consider whether the input is less than 8; output 1 (if it is) or 0 (if it is not). Here are some jump tests that take an input, then output 0 if the input was zero or 1 if the input was non-zero: 3,12,6,12,15,1,13,14,13,4,13,99,-1,0,1,9 (using position mode) 3,3,1105,-1,9,1101,0,0,12,4,12,99,1 (using immediate mode) Here's a larger example: 3,21,1008,21,8,20,1005,20,22,107,8,21,20,1006,20,31, 1106,0,36,98,0,0,1002,21,125,20,4,20,1105,1,46,104, 999,1105,1,46,1101,1000,1,20,4,20,1105,1,46,98,99 The above example program uses an input instruction to ask for a single number. The program will then output 999 if the input value is below 8, output 1000 if the input value is equal to 8, or output 1001 if the input value is greater than 8. This time, when the TEST diagnostic program runs its input instruction to get the ID of the system to test, provide it 5, the ID for the ship's thermal radiator controller. This diagnostic test suite only outputs one number, the diagnostic code. What is the diagnostic code for system ID 5?	39
--- Day 24: Blizzard Basin --- With everything replanted for next year (and with elephants and monkeys to tend the grove), you and the Elves leave for the extraction point. Partway up the mountain that shields the grove is a flat, open area that serves as the extraction point. It's a bit of a climb, but nothing the expedition can't handle. At least, that would normally be true; now that the mountain is covered in snow, things have become more difficult than the Elves are used to. As the expedition reaches a valley that must be traversed to reach the extraction site, you find that strong, turbulent winds are pushing small blizzards of snow and sharp ice around the valley. It's a good thing everyone packed warm clothes! To make it across safely, you'll need to find a way to avoid them. Fortunately, it's easy to see all of this from the entrance to the valley, so you make a map of the valley and the blizzards (your puzzle input). For example: #.##### #.....# #>....# #.....# #...v.# #.....# #####.# The walls of the valley are drawn as #; everything else is ground. Clear ground - where there is currently no blizzard - is drawn as .. Otherwise, blizzards are drawn with an arrow indicating their direction of motion: up (^), down (v), left (<), or right (>). The above map includes two blizzards, one moving right (>) and one moving down (v). In one minute, each blizzard moves one position in the direction it is pointing: #.##### #.....# #.>...# #.....# #.....# #...v.# #####.# Due to conservation of blizzard energy, as a blizzard reaches the wall of the valley, a new blizzard forms on the opposite side of the valley moving in the same direction. After another minute, the bottom downward-moving blizzard has been replaced with a new downward-moving blizzard at the top of the valley instead: #.##### #...v.# #..>..# #.....# #.....# #.....# #####.# Because blizzards are made of tiny snowflakes, they pass right through each other. After another minute, both blizzards temporarily occupy the same position, marked 2: #.##### #.....# #...2.# #.....# #.....# #.....# #####.# After another minute, the situation resolves itself, giving each blizzard back its personal space: #.##### #.....# #....># #...v.# #.....# #.....# #####.# Finally, after yet another minute, the rightward-facing blizzard on the right is replaced with a new one on the left facing the same direction: #.##### #.....# #>....# #.....# #...v.# #.....# #####.# This process repeats at least as long as you are observing it, but probably forever. Here is a more complex example: #.###### #>>.<^<# #.<..<<# #>v.><># #<^v^^># ######.# Your expedition begins in the only non-wall position in the top row and needs to reach the only non-wall position in the bottom row. On each minute, you can move up, down, left, or right, or you can wait in place. You and the blizzards act simultaneously, and you cannot share a position with a blizzard. In the above example, the fastest way to reach your goal requires 18 steps. Drawing the position of the expedition as E, one way to achieve this is: Initial state: #E###### #>>.<^<# #.<..<<# #>v.><># #<^v^^># ######.# Minute 1, move down: #.###### #E>3.<.# #<..<<.# #>2.22.# #>v..^<# ######.# Minute 2, move down: #.###### #.2>2..# #E^22^<# #.>2.^># #.>..<.# ######.# Minute 3, wait: #.###### #<^<22.# #E2<.2.# #><2>..# #..><..# ######.# Minute 4, move up: #.###### #E<..22# #<<.<..# #<2.>>.# #.^22^.# ######.# Minute 5, move right: #.###### #2Ev.<># #<.<..<# #.^>^22# #.2..2.# ######.# Minute 6, move right: #.###### #>2E<.<# #.2v^2<# #>..>2># #<....># ######.# Minute 7, move down: #.###### #.22^2.# #<vE<2.# #>>v<>.# #>....<# ######.# Minute 8, move left: #.###### #.<>2^.# #.E<<.<# #.22..># #.2v^2.# ######.# Minute 9, move up: #.###### #<E2>>.# #.<<.<.# #>2>2^.# #.v><^.# ######.# Minute 10, move right: #.###### #.2E.>2# #<2v2^.# #<>.>2.# #..<>..# ######.# Minute 11, wait: #.###### #2^E^2># #<v<.^<# #..2.>2# #.<..>.# ######.# Minute 12, move down: #.###### #>>.<^<# #.<E.<<# #>v.><># #<^v^^># ######.# Minute 13, move down: #.###### #.>3.<.# #<..<<.# #>2E22.# #>v..^<# ######.# Minute 14, move right: #.###### #.2>2..# #.^22^<# #.>2E^># #.>..<.# ######.# Minute 15, move right: #.###### #<^<22.# #.2<.2.# #><2>E.# #..><..# ######.# Minute 16, move right: #.###### #.<..22# #<<.<..# #<2.>>E# #.^22^.# ######.# Minute 17, move down: #.###### #2.v.<># #<.<..<# #.^>^22# #.2..2E# ######.# Minute 18, move down: #.###### #>2.<.<# #.2v^2<# #>..>2># #<....># ######E# What is the fewest number of minutes required to avoid the blizzards and reach the goal? Your puzzle answer was 299. --- Part Two --- As the expedition reaches the far side of the valley, one of the Elves looks especially dismayed: He forgot his snacks at the entrance to the valley! Since you're so good at dodging blizzards, the Elves humbly request that you go back for his snacks. From the same initial conditions, how quickly can you make it from the start to the goal, then back to the start, then back to the goal? In the above example, the first trip to the goal takes 18 minutes, the trip back to the start takes 23 minutes, and the trip back to the goal again takes 13 minutes, for a total time of 54 minutes. What is the fewest number of minutes required to reach the goal, go back to the start, then reach the goal again?	40
--- Day 7: No Space Left On Device --- You can hear birds chirping and raindrops hitting leaves as the expedition proceeds. Occasionally, you can even hear much louder sounds in the distance; how big do the animals get out here, anyway? The device the Elves gave you has problems with more than just its communication system. You try to run a system update: $ system-update --please --pretty-please-with-sugar-on-top Error: No space left on device Perhaps you can delete some files to make space for the update? You browse around the filesystem to assess the situation and save the resulting terminal output (your puzzle input). For example: $ cd / $ ls dir a 14848514 b.txt 8504156 c.dat dir d $ cd a $ ls dir e 29116 f 2557 g 62596 h.lst $ cd e $ ls 584 i $ cd .. $ cd .. $ cd d $ ls 4060174 j 8033020 d.log 5626152 d.ext 7214296 k The filesystem consists of a tree of files (plain data) and directories (which can contain other directories or files). The outermost directory is called /. You can navigate around the filesystem, moving into or out of directories and listing the contents of the directory you're currently in. Within the terminal output, lines that begin with $ are commands you executed, very much like some modern computers: cd means change directory. This changes which directory is the current directory, but the specific result depends on the argument: cd x moves in one level: it looks in the current directory for the directory named x and makes it the current directory. cd .. moves out one level: it finds the directory that contains the current directory, then makes that directory the current directory. cd / switches the current directory to the outermost directory, /. ls means list. It prints out all of the files and directories immediately contained by the current directory: 123 abc means that the current directory contains a file named abc with size 123. dir xyz means that the current directory contains a directory named xyz. Given the commands and output in the example above, you can determine that the filesystem looks visually like this: - / (dir) - a (dir) - e (dir) - i (file, size=584) - f (file, size=29116) - g (file, size=2557) - h.lst (file, size=62596) - b.txt (file, size=14848514) - c.dat (file, size=8504156) - d (dir) - j (file, size=4060174) - d.log (file, size=8033020) - d.ext (file, size=5626152) - k (file, size=7214296) Here, there are four directories: / (the outermost directory), a and d (which are in /), and e (which is in a). These directories also contain files of various sizes. Since the disk is full, your first step should probably be to find directories that are good candidates for deletion. To do this, you need to determine the total size of each directory. The total size of a directory is the sum of the sizes of the files it contains, directly or indirectly. (Directories themselves do not count as having any intrinsic size.) The total sizes of the directories above can be found as follows: The total size of directory e is 584 because it contains a single file i of size 584 and no other directories. The directory a has total size 94853 because it contains files f (size 29116), g (size 2557), and h.lst (size 62596), plus file i indirectly (a contains e which contains i). Directory d has total size 24933642. As the outermost directory, / contains every file. Its total size is 48381165, the sum of the size of every file. To begin, find all of the directories with a total size of at most 100000, then calculate the sum of their total sizes. In the example above, these directories are a and e; the sum of their total sizes is 95437 (94853 + 584). (As in this example, this process can count files more than once!) Find all of the directories with a total size of at most 100000. What is the sum of the total sizes of those directories?	41
--- Day 12: Garden Groups --- Why not search for the Chief Historian near the gardener and his massive farm? There's plenty of food, so The Historians grab something to eat while they search. You're about to settle near a complex arrangement of garden plots when some Elves ask if you can lend a hand. They'd like to set up fences around each region of garden plots, but they can't figure out how much fence they need to order or how much it will cost. They hand you a map (your puzzle input) of the garden plots. Each garden plot grows only a single type of plant and is indicated by a single letter on your map. When multiple garden plots are growing the same type of plant and are touching (horizontally or vertically), they form a region. For example: AAAA BBCD BBCC EEEC This 4x4 arrangement includes garden plots growing five different types of plants (labeled A, B, C, D, and E), each grouped into their own region. In order to accurately calculate the cost of the fence around a single region, you need to know that region's area and perimeter. The area of a region is simply the number of garden plots the region contains. The above map's type A, B, and C plants are each in a region of area 4. The type E plants are in a region of area 3; the type D plants are in a region of area 1. Each garden plot is a square and so has four sides. The perimeter of a region is the number of sides of garden plots in the region that do not touch another garden plot in the same region. The type A and C plants are each in a region with perimeter 10. The type B and E plants are each in a region with perimeter 8. The lone D plot forms its own region with perimeter 4. Visually indicating the sides of plots in each region that contribute to the perimeter using - and \|, the above map's regions' perimeters are measured as follows: +-+-+-+-+ \|A A A A\| +-+-+-+-+ +-+ \|D\| +-+-+ +-+ +-+ \|B B\| \|C\| + + + +-+ \|B B\| \|C C\| +-+-+ +-+ + \|C\| +-+-+-+ +-+ \|E E E\| +-+-+-+ Plants of the same type can appear in multiple separate regions, and regions can even appear within other regions. For example: OOOOO OXOXO OOOOO OXOXO OOOOO The above map contains five regions, one containing all of the O garden plots, and the other four each containing a single X plot. The four X regions each have area 1 and perimeter 4. The region containing 21 type O plants is more complicated; in addition to its outer edge contributing a perimeter of 20, its boundary with each X region contributes an additional 4 to its perimeter, for a total perimeter of 36. Due to "modern" business practices, the price of fence required for a region is found by multiplying that region's area by its perimeter. The total price of fencing all regions on a map is found by adding together the price of fence for every region on the map. In the first example, region A has price 4 * 10 = 40, region B has price 4 * 8 = 32, region C has price 4 * 10 = 40, region D has price 1 * 4 = 4, and region E has price 3 * 8 = 24. So, the total price for the first example is 140. In the second example, the region with all of the O plants has price 21 * 36 = 756, and each of the four smaller X regions has price 1 * 4 = 4, for a total price of 772 (756 + 4 + 4 + 4 + 4). Here's a larger example: RRRRIICCFF RRRRIICCCF VVRRRCCFFF VVRCCCJFFF VVVVCJJCFE VVIVCCJJEE VVIIICJJEE MIIIIIJJEE MIIISIJEEE MMMISSJEEE It contains: A region of R plants with price 12 * 18 = 216. A region of I plants with price 4 * 8 = 32. A region of C plants with price 14 * 28 = 392. A region of F plants with price 10 * 18 = 180. A region of V plants with price 13 * 20 = 260. A region of J plants with price 11 * 20 = 220. A region of C plants with price 1 * 4 = 4. A region of E plants with price 13 * 18 = 234. A region of I plants with price 14 * 22 = 308. A region of M plants with price 5 * 12 = 60. A region of S plants with price 3 * 8 = 24. So, it has a total price of 1930. What is the total price of fencing all regions on your map?	42
--- Day 14: Extended Polymerization --- The incredible pressures at this depth are starting to put a strain on your submarine. The submarine has polymerization equipment that would produce suitable materials to reinforce the submarine, and the nearby volcanically-active caves should even have the necessary input elements in sufficient quantities. The submarine manual contains instructions for finding the optimal polymer formula; specifically, it offers a polymer template and a list of pair insertion rules (your puzzle input). You just need to work out what polymer would result after repeating the pair insertion process a few times. For example: NNCB CH -> B HH -> N CB -> H NH -> C HB -> C HC -> B HN -> C NN -> C BH -> H NC -> B NB -> B BN -> B BB -> N BC -> B CC -> N CN -> C The first line is the polymer template - this is the starting point of the process. The following section defines the pair insertion rules. A rule like AB -> C means that when elements A and B are immediately adjacent, element C should be inserted between them. These insertions all happen simultaneously. So, starting with the polymer template NNCB, the first step simultaneously considers all three pairs: The first pair (NN) matches the rule NN -> C, so element C is inserted between the first N and the second N. The second pair (NC) matches the rule NC -> B, so element B is inserted between the N and the C. The third pair (CB) matches the rule CB -> H, so element H is inserted between the C and the B. Note that these pairs overlap: the second element of one pair is the first element of the next pair. Also, because all pairs are considered simultaneously, inserted elements are not considered to be part of a pair until the next step. After the first step of this process, the polymer becomes NCNBCHB. Here are the results of a few steps using the above rules: Template: NNCB After step 1: NCNBCHB After step 2: NBCCNBBBCBHCB After step 3: NBBBCNCCNBBNBNBBCHBHHBCHB After step 4: NBBNBNBBCCNBCNCCNBBNBBNBBBNBBNBBCBHCBHHNHCBBCBHCB This polymer grows quickly. After step 5, it has length 97; After step 10, it has length 3073. After step 10, B occurs 1749 times, C occurs 298 times, H occurs 161 times, and N occurs 865 times; taking the quantity of the most common element (B, 1749) and subtracting the quantity of the least common element (H, 161) produces 1749 - 161 = 1588. Apply 10 steps of pair insertion to the polymer template and find the most and least common elements in the result. What do you get if you take the quantity of the most common element and subtract the quantity of the least common element? Your puzzle answer was 2915. --- Part Two --- The resulting polymer isn't nearly strong enough to reinforce the submarine. You'll need to run more steps of the pair insertion process; a total of 40 steps should do it. In the above example, the most common element is B (occurring 2192039569602 times) and the least common element is H (occurring 3849876073 times); subtracting these produces 2188189693529. Apply 40 steps of pair insertion to the polymer template and find the most and least common elements in the result. What do you get if you take the quantity of the most common element and subtract the quantity of the least common element?	43
--- Day 17: Pyroclastic Flow --- Your handheld device has located an alternative exit from the cave for you and the elephants. The ground is rumbling almost continuously now, but the strange valves bought you some time. It's definitely getting warmer in here, though. The tunnels eventually open into a very tall, narrow chamber. Large, oddly-shaped rocks are falling into the chamber from above, presumably due to all the rumbling. If you can't work out where the rocks will fall next, you might be crushed! The five types of rocks have the following peculiar shapes, where # is rock and . is empty space: #### .#. ### .#. ..# ..# ### # # # # ## ## The rocks fall in the order shown above: first the - shape, then the + shape, and so on. Once the end of the list is reached, the same order repeats: the - shape falls first, sixth, 11th, 16th, etc. The rocks don't spin, but they do get pushed around by jets of hot gas coming out of the walls themselves. A quick scan reveals the effect the jets of hot gas will have on the rocks as they fall (your puzzle input). For example, suppose this was the jet pattern in your cave: >>><<><>><<<>><>>><<<>>><<<><<<>><>><<>> In jet patterns, < means a push to the left, while > means a push to the right. The pattern above means that the jets will push a falling rock right, then right, then right, then left, then left, then right, and so on. If the end of the list is reached, it repeats. The tall, vertical chamber is exactly seven units wide. Each rock appears so that its left edge is two units away from the left wall and its bottom edge is three units above the highest rock in the room (or the floor, if there isn't one). After a rock appears, it alternates between being pushed by a jet of hot gas one unit (in the direction indicated by the next symbol in the jet pattern) and then falling one unit down. If any movement would cause any part of the rock to move into the walls, floor, or a stopped rock, the movement instead does not occur. If a downward movement would have caused a falling rock to move into the floor or an already-fallen rock, the falling rock stops where it is (having landed on something) and a new rock immediately begins falling. Drawing falling rocks with @ and stopped rocks with #, the jet pattern in the example above manifests as follows: The first rock begins falling: \|..@@@@.\| \|.......\| \|.......\| \|.......\| +-------+ Jet of gas pushes rock right: \|...@@@@\| \|.......\| \|.......\| \|.......\| +-------+ Rock falls 1 unit: \|...@@@@\| \|.......\| \|.......\| +-------+ Jet of gas pushes rock right, but nothing happens: \|...@@@@\| \|.......\| \|.......\| +-------+ Rock falls 1 unit: \|...@@@@\| \|.......\| +-------+ Jet of gas pushes rock right, but nothing happens: \|...@@@@\| \|.......\| +-------+ Rock falls 1 unit: \|...@@@@\| +-------+ Jet of gas pushes rock left: \|..@@@@.\| +-------+ Rock falls 1 unit, causing it to come to rest: \|..####.\| +-------+ A new rock begins falling: \|...@...\| \|..@@@..\| \|...@...\| \|.......\| \|.......\| \|.......\| \|..####.\| +-------+ Jet of gas pushes rock left: \|..@....\| \|.@@@...\| \|..@....\| \|.......\| \|.......\| \|.......\| \|..####.\| +-------+ Rock falls 1 unit: \|..@....\| \|.@@@...\| \|..@....\| \|.......\| \|.......\| \|..####.\| +-------+ Jet of gas pushes rock right: \|...@...\| \|..@@@..\| \|...@...\| \|.......\| \|.......\| \|..####.\| +-------+ Rock falls 1 unit: \|...@...\| \|..@@@..\| \|...@...\| \|.......\| \|..####.\| +-------+ Jet of gas pushes rock left: \|..@....\| \|.@@@...\| \|..@....\| \|.......\| \|..####.\| +-------+ Rock falls 1 unit: \|..@....\| \|.@@@...\| \|..@....\| \|..####.\| +-------+ Jet of gas pushes rock right: \|...@...\| \|..@@@..\| \|...@...\| \|..####.\| +-------+ Rock falls 1 unit, causing it to come to rest: \|...#...\| \|..###..\| \|...#...\| \|..####.\| +-------+ A new rock begins falling: \|....@..\| \|....@..\| \|..@@@..\| \|.......\| \|.......\| \|.......\| \|...#...\| \|..###..\| \|...#...\| \|..####.\| +-------+ The moment each of the next few rocks begins falling, you would see this: \|..@....\| \|..@....\| \|..@....\| \|..@....\| \|.......\| \|.......\| \|.......\| \|..#....\| \|..#....\| \|####...\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|..@@...\| \|..@@...\| \|.......\| \|.......\| \|.......\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|..@@@@.\| \|.......\| \|.......\| \|.......\| \|....##.\| \|....##.\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|...@...\| \|..@@@..\| \|...@...\| \|.......\| \|.......\| \|.......\| \|.####..\| \|....##.\| \|....##.\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|....@..\| \|....@..\| \|..@@@..\| \|.......\| \|.......\| \|.......\| \|..#....\| \|.###...\| \|..#....\| \|.####..\| \|....##.\| \|....##.\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|..@....\| \|..@....\| \|..@....\| \|..@....\| \|.......\| \|.......\| \|.......\| \|.....#.\| \|.....#.\| \|..####.\| \|.###...\| \|..#....\| \|.####..\| \|....##.\| \|....##.\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|..@@...\| \|..@@...\| \|.......\| \|.......\| \|.......\| \|....#..\| \|....#..\| \|....##.\| \|....##.\| \|..####.\| \|.###...\| \|..#....\| \|.####..\| \|....##.\| \|....##.\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|..@@@@.\| \|.......\| \|.......\| \|.......\| \|....#..\| \|....#..\| \|....##.\| \|##..##.\| \|######.\| \|.###...\| \|..#....\| \|.####..\| \|....##.\| \|....##.\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ To prove to the elephants your simulation is accurate, they want to know how tall the tower will get after 2022 rocks have stopped (but before the 2023rd rock begins falling). In this example, the tower of rocks will be 3068 units tall. How many units tall will the tower of rocks be after 2022 rocks have stopped falling? Your puzzle answer was 3098. --- Part Two --- The elephants are not impressed by your simulation. They demand to know how tall the tower will be after 1000000000000 rocks have stopped! Only then will they feel confident enough to proceed through the cave. In the example above, the tower would be 1514285714288 units tall! How tall will the tower be after 1000000000000 rocks have stopped?	44
--- Day 22: Monkey Map --- The monkeys take you on a surprisingly easy trail through the jungle. They're even going in roughly the right direction according to your handheld device's Grove Positioning System. As you walk, the monkeys explain that the grove is protected by a force field. To pass through the force field, you have to enter a password; doing so involves tracing a specific path on a strangely-shaped board. At least, you're pretty sure that's what you have to do; the elephants aren't exactly fluent in monkey. The monkeys give you notes that they took when they last saw the password entered (your puzzle input). For example: ...# .#.. #... .... ...#.......# ........#... ..#....#.... ..........#. ...#.... .....#.. .#...... ......#. 10R5L5R10L4R5L5 The first half of the monkeys' notes is a map of the board. It is comprised of a set of open tiles (on which you can move, drawn .) and solid walls (tiles which you cannot enter, drawn #). The second half is a description of the path you must follow. It consists of alternating numbers and letters: A number indicates the number of tiles to move in the direction you are facing. If you run into a wall, you stop moving forward and continue with the next instruction. A letter indicates whether to turn 90 degrees clockwise (R) or counterclockwise (L). Turning happens in-place; it does not change your current tile. So, a path like 10R5 means "go forward 10 tiles, then turn clockwise 90 degrees, then go forward 5 tiles". You begin the path in the leftmost open tile of the top row of tiles. Initially, you are facing to the right (from the perspective of how the map is drawn). If a movement instruction would take you off of the map, you wrap around to the other side of the board. In other words, if your next tile is off of the board, you should instead look in the direction opposite of your current facing as far as you can until you find the opposite edge of the board, then reappear there. For example, if you are at A and facing to the right, the tile in front of you is marked B; if you are at C and facing down, the tile in front of you is marked D: ...# .#.. #... .... ...#.D.....# ........#... B.#....#...A .....C....#. ...#.... .....#.. .#...... ......#. It is possible for the next tile (after wrapping around) to be a wall; this still counts as there being a wall in front of you, and so movement stops before you actually wrap to the other side of the board. By drawing the last facing you had with an arrow on each tile you visit, the full path taken by the above example looks like this: >>v# .#v. #.v. ..v. ...#...v..v# >>>v...>#.>> ..#v...#.... ...>>>>v..#. ...#.... .....#.. .#...... ......#. To finish providing the password to this strange input device, you need to determine numbers for your final row, column, and facing as your final position appears from the perspective of the original map. Rows start from 1 at the top and count downward; columns start from 1 at the left and count rightward. (In the above example, row 1, column 1 refers to the empty space with no tile on it in the top-left corner.) Facing is 0 for right (>), 1 for down (v), 2 for left (<), and 3 for up (^). The final password is the sum of 1000 times the row, 4 times the column, and the facing. In the above example, the final row is 6, the final column is 8, and the final facing is 0. So, the final password is 1000 * 6 + 4 * 8 + 0: 6032. Follow the path given in the monkeys' notes. What is the final password? Your puzzle answer was 11464. --- Part Two --- As you reach the force field, you think you hear some Elves in the distance. Perhaps they've already arrived? You approach the strange input device, but it isn't quite what the monkeys drew in their notes. Instead, you are met with a large cube; each of its six faces is a square of 50x50 tiles. To be fair, the monkeys' map does have six 50x50 regions on it. If you were to carefully fold the map, you should be able to shape it into a cube! In the example above, the six (smaller, 4x4) faces of the cube are: 1111 1111 1111 1111 222233334444 222233334444 222233334444 222233334444 55556666 55556666 55556666 55556666 You still start in the same position and with the same facing as before, but the wrapping rules are different. Now, if you would walk off the board, you instead proceed around the cube. From the perspective of the map, this can look a little strange. In the above example, if you are at A and move to the right, you would arrive at B facing down; if you are at C and move down, you would arrive at D facing up: ...# .#.. #... .... ...#.......# ........#..A ..#....#.... .D........#. ...#..B. .....#.. .#...... ..C...#. Walls still block your path, even if they are on a different face of the cube. If you are at E facing up, your movement is blocked by the wall marked by the arrow: ...# .#.. -->#... .... ...#..E....# ........#... ..#....#.... ..........#. ...#.... .....#.. .#...... ......#. Using the same method of drawing the last facing you had with an arrow on each tile you visit, the full path taken by the above example now looks like this: >>v# .#v. #.v. ..v. ...#..^...v# .>>>>>^.#.>> .^#....#.... .^........#. ...#..v. .....#v. .#v<<<<. ..v...#. The final password is still calculated from your final position and facing from the perspective of the map. In this example, the final row is 5, the final column is 7, and the final facing is 3, so the final password is 1000 * 5 + 4 * 7 + 3 = 5031. Fold the map into a cube, then follow the path given in the monkeys' notes. What is the final password?	45
--- Day 19: Not Enough Minerals --- Your scans show that the lava did indeed form obsidian! The wind has changed direction enough to stop sending lava droplets toward you, so you and the elephants exit the cave. As you do, you notice a collection of geodes around the pond. Perhaps you could use the obsidian to create some geode-cracking robots and break them open? To collect the obsidian from the bottom of the pond, you'll need waterproof obsidian-collecting robots. Fortunately, there is an abundant amount of clay nearby that you can use to make them waterproof. In order to harvest the clay, you'll need special-purpose clay-collecting robots. To make any type of robot, you'll need ore, which is also plentiful but in the opposite direction from the clay. Collecting ore requires ore-collecting robots with big drills. Fortunately, you have exactly one ore-collecting robot in your pack that you can use to kickstart the whole operation. Each robot can collect 1 of its resource type per minute. It also takes one minute for the robot factory (also conveniently from your pack) to construct any type of robot, although it consumes the necessary resources available when construction begins. The robot factory has many blueprints (your puzzle input) you can choose from, but once you've configured it with a blueprint, you can't change it. You'll need to work out which blueprint is best. For example: Blueprint 1: Each ore robot costs 4 ore. Each clay robot costs 2 ore. Each obsidian robot costs 3 ore and 14 clay. Each geode robot costs 2 ore and 7 obsidian. Blueprint 2: Each ore robot costs 2 ore. Each clay robot costs 3 ore. Each obsidian robot costs 3 ore and 8 clay. Each geode robot costs 3 ore and 12 obsidian. (Blueprints have been line-wrapped here for legibility. The robot factory's actual assortment of blueprints are provided one blueprint per line.) The elephants are starting to look hungry, so you shouldn't take too long; you need to figure out which blueprint would maximize the number of opened geodes after 24 minutes by figuring out which robots to build and when to build them. Using blueprint 1 in the example above, the largest number of geodes you could open in 24 minutes is 9. One way to achieve that is: == Minute 1 == 1 ore-collecting robot collects 1 ore; you now have 1 ore. == Minute 2 == 1 ore-collecting robot collects 1 ore; you now have 2 ore. == Minute 3 == Spend 2 ore to start building a clay-collecting robot. 1 ore-collecting robot collects 1 ore; you now have 1 ore. The new clay-collecting robot is ready; you now have 1 of them. == Minute 4 == 1 ore-collecting robot collects 1 ore; you now have 2 ore. 1 clay-collecting robot collects 1 clay; you now have 1 clay. == Minute 5 == Spend 2 ore to start building a clay-collecting robot. 1 ore-collecting robot collects 1 ore; you now have 1 ore. 1 clay-collecting robot collects 1 clay; you now have 2 clay. The new clay-collecting robot is ready; you now have 2 of them. == Minute 6 == 1 ore-collecting robot collects 1 ore; you now have 2 ore. 2 clay-collecting robots collect 2 clay; you now have 4 clay. == Minute 7 == Spend 2 ore to start building a clay-collecting robot. 1 ore-collecting robot collects 1 ore; you now have 1 ore. 2 clay-collecting robots collect 2 clay; you now have 6 clay. The new clay-collecting robot is ready; you now have 3 of them. == Minute 8 == 1 ore-collecting robot collects 1 ore; you now have 2 ore. 3 clay-collecting robots collect 3 clay; you now have 9 clay. == Minute 9 == 1 ore-collecting robot collects 1 ore; you now have 3 ore. 3 clay-collecting robots collect 3 clay; you now have 12 clay. == Minute 10 == 1 ore-collecting robot collects 1 ore; you now have 4 ore. 3 clay-collecting robots collect 3 clay; you now have 15 clay. == Minute 11 == Spend 3 ore and 14 clay to start building an obsidian-collecting robot. 1 ore-collecting robot collects 1 ore; you now have 2 ore. 3 clay-collecting robots collect 3 clay; you now have 4 clay. The new obsidian-collecting robot is ready; you now have 1 of them. == Minute 12 == Spend 2 ore to start building a clay-collecting robot. 1 ore-collecting robot collects 1 ore; you now have 1 ore. 3 clay-collecting robots collect 3 clay; you now have 7 clay. 1 obsidian-collecting robot collects 1 obsidian; you now have 1 obsidian. The new clay-collecting robot is ready; you now have 4 of them. == Minute 13 == 1 ore-collecting robot collects 1 ore; you now have 2 ore. 4 clay-collecting robots collect 4 clay; you now have 11 clay. 1 obsidian-collecting robot collects 1 obsidian; you now have 2 obsidian. == Minute 14 == 1 ore-collecting robot collects 1 ore; you now have 3 ore. 4 clay-collecting robots collect 4 clay; you now have 15 clay. 1 obsidian-collecting robot collects 1 obsidian; you now have 3 obsidian. == Minute 15 == Spend 3 ore and 14 clay to start building an obsidian-collecting robot. 1 ore-collecting robot collects 1 ore; you now have 1 ore. 4 clay-collecting robots collect 4 clay; you now have 5 clay. 1 obsidian-collecting robot collects 1 obsidian; you now have 4 obsidian. The new obsidian-collecting robot is ready; you now have 2 of them. == Minute 16 == 1 ore-collecting robot collects 1 ore; you now have 2 ore. 4 clay-collecting robots collect 4 clay; you now have 9 clay. 2 obsidian-collecting robots collect 2 obsidian; you now have 6 obsidian. == Minute 17 == 1 ore-collecting robot collects 1 ore; you now have 3 ore. 4 clay-collecting robots collect 4 clay; you now have 13 clay. 2 obsidian-collecting robots collect 2 obsidian; you now have 8 obsidian. == Minute 18 == Spend 2 ore and 7 obsidian to start building a geode-cracking robot. 1 ore-collecting robot collects 1 ore; you now have 2 ore. 4 clay-collecting robots collect 4 clay; you now have 17 clay. 2 obsidian-collecting robots collect 2 obsidian; you now have 3 obsidian. The new geode-cracking robot is ready; you now have 1 of them. == Minute 19 == 1 ore-collecting robot collects 1 ore; you now have 3 ore. 4 clay-collecting robots collect 4 clay; you now have 21 clay. 2 obsidian-collecting robots collect 2 obsidian; you now have 5 obsidian. 1 geode-cracking robot cracks 1 geode; you now have 1 open geode. == Minute 20 == 1 ore-collecting robot collects 1 ore; you now have 4 ore. 4 clay-collecting robots collect 4 clay; you now have 25 clay. 2 obsidian-collecting robots collect 2 obsidian; you now have 7 obsidian. 1 geode-cracking robot cracks 1 geode; you now have 2 open geodes. == Minute 21 == Spend 2 ore and 7 obsidian to start building a geode-cracking robot. 1 ore-collecting robot collects 1 ore; you now have 3 ore. 4 clay-collecting robots collect 4 clay; you now have 29 clay. 2 obsidian-collecting robots collect 2 obsidian; you now have 2 obsidian. 1 geode-cracking robot cracks 1 geode; you now have 3 open geodes. The new geode-cracking robot is ready; you now have 2 of them. == Minute 22 == 1 ore-collecting robot collects 1 ore; you now have 4 ore. 4 clay-collecting robots collect 4 clay; you now have 33 clay. 2 obsidian-collecting robots collect 2 obsidian; you now have 4 obsidian. 2 geode-cracking robots crack 2 geodes; you now have 5 open geodes. == Minute 23 == 1 ore-collecting robot collects 1 ore; you now have 5 ore. 4 clay-collecting robots collect 4 clay; you now have 37 clay. 2 obsidian-collecting robots collect 2 obsidian; you now have 6 obsidian. 2 geode-cracking robots crack 2 geodes; you now have 7 open geodes. == Minute 24 == 1 ore-collecting robot collects 1 ore; you now have 6 ore. 4 clay-collecting robots collect 4 clay; you now have 41 clay. 2 obsidian-collecting robots collect 2 obsidian; you now have 8 obsidian. 2 geode-cracking robots crack 2 geodes; you now have 9 open geodes. However, by using blueprint 2 in the example above, you could do even better: the largest number of geodes you could open in 24 minutes is 12. Determine the quality level of each blueprint by multiplying that blueprint's ID number with the largest number of geodes that can be opened in 24 minutes using that blueprint. In this example, the first blueprint has ID 1 and can open 9 geodes, so its quality level is 9. The second blueprint has ID 2 and can open 12 geodes, so its quality level is 24. Finally, if you add up the quality levels of all of the blueprints in the list, you get 33. Determine the quality level of each blueprint using the largest number of geodes it could produce in 24 minutes. What do you get if you add up the quality level of all of the blueprints in your list? Your puzzle answer was 1466. --- Part Two --- While you were choosing the best blueprint, the elephants found some food on their own, so you're not in as much of a hurry; you figure you probably have 32 minutes before the wind changes direction again and you'll need to get out of range of the erupting volcano. Unfortunately, one of the elephants ate most of your blueprint list! Now, only the first three blueprints in your list are intact. In 32 minutes, the largest number of geodes blueprint 1 (from the example above) can open is 56. One way to achieve that is: == Minute 1 == 1 ore-collecting robot collects 1 ore; you now have 1 ore. == Minute 2 == 1 ore-collecting robot collects 1 ore; you now have 2 ore. == Minute 3 == 1 ore-collecting robot collects 1 ore; you now have 3 ore. == Minute 4 == 1 ore-collecting robot collects 1 ore; you now have 4 ore. == Minute 5 == Spend 4 ore to start building an ore-collecting robot. 1 ore-collecting robot collects 1 ore; you now have 1 ore. The new ore-collecting robot is ready; you now have 2 of them. == Minute 6 == 2 ore-collecting robots collect 2 ore; you now have 3 ore. == Minute 7 == Spend 2 ore to start building a clay-collecting robot. 2 ore-collecting robots collect 2 ore; you now have 3 ore. The new clay-collecting robot is ready; you now have 1 of them. == Minute 8 == Spend 2 ore to start building a clay-collecting robot. 2 ore-collecting robots collect 2 ore; you now have 3 ore. 1 clay-collecting robot collects 1 clay; you now have 1 clay. The new clay-collecting robot is ready; you now have 2 of them. == Minute 9 == Spend 2 ore to start building a clay-collecting robot. 2 ore-collecting robots collect 2 ore; you now have 3 ore. 2 clay-collecting robots collect 2 clay; you now have 3 clay. The new clay-collecting robot is ready; you now have 3 of them. == Minute 10 == Spend 2 ore to start building a clay-collecting robot. 2 ore-collecting robots collect 2 ore; you now have 3 ore. 3 clay-collecting robots collect 3 clay; you now have 6 clay. The new clay-collecting robot is ready; you now have 4 of them. == Minute 11 == Spend 2 ore to start building a clay-collecting robot. 2 ore-collecting robots collect 2 ore; you now have 3 ore. 4 clay-collecting robots collect 4 clay; you now have 10 clay. The new clay-collecting robot is ready; you now have 5 of them. == Minute 12 == Spend 2 ore to start building a clay-collecting robot. 2 ore-collecting robots collect 2 ore; you now have 3 ore. 5 clay-collecting robots collect 5 clay; you now have 15 clay. The new clay-collecting robot is ready; you now have 6 of them. == Minute 13 == Spend 2 ore to start building a clay-collecting robot. 2 ore-collecting robots collect 2 ore; you now have 3 ore. 6 clay-collecting robots collect 6 clay; you now have 21 clay. The new clay-collecting robot is ready; you now have 7 of them. == Minute 14 == Spend 3 ore and 14 clay to start building an obsidian-collecting robot. 2 ore-collecting robots collect 2 ore; you now have 2 ore. 7 clay-collecting robots collect 7 clay; you now have 14 clay. The new obsidian-collecting robot is ready; you now have 1 of them. == Minute 15 == 2 ore-collecting robots collect 2 ore; you now have 4 ore. 7 clay-collecting robots collect 7 clay; you now have 21 clay. 1 obsidian-collecting robot collects 1 obsidian; you now have 1 obsidian. == Minute 16 == Spend 3 ore and 14 clay to start building an obsidian-collecting robot. 2 ore-collecting robots collect 2 ore; you now have 3 ore. 7 clay-collecting robots collect 7 clay; you now have 14 clay. 1 obsidian-collecting robot collects 1 obsidian; you now have 2 obsidian. The new obsidian-collecting robot is ready; you now have 2 of them. == Minute 17 == Spend 3 ore and 14 clay to start building an obsidian-collecting robot. 2 ore-collecting robots collect 2 ore; you now have 2 ore. 7 clay-collecting robots collect 7 clay; you now have 7 clay. 2 obsidian-collecting robots collect 2 obsidian; you now have 4 obsidian. The new obsidian-collecting robot is ready; you now have 3 of them. == Minute 18 == 2 ore-collecting robots collect 2 ore; you now have 4 ore. 7 clay-collecting robots collect 7 clay; you now have 14 clay. 3 obsidian-collecting robots collect 3 obsidian; you now have 7 obsidian. == Minute 19 == Spend 3 ore and 14 clay to start building an obsidian-collecting robot. 2 ore-collecting robots collect 2 ore; you now have 3 ore. 7 clay-collecting robots collect 7 clay; you now have 7 clay. 3 obsidian-collecting robots collect 3 obsidian; you now have 10 obsidian. The new obsidian-collecting robot is ready; you now have 4 of them. == Minute 20 == Spend 2 ore and 7 obsidian to start building a geode-cracking robot. 2 ore-collecting robots collect 2 ore; you now have 3 ore. 7 clay-collecting robots collect 7 clay; you now have 14 clay. 4 obsidian-collecting robots collect 4 obsidian; you now have 7 obsidian. The new geode-cracking robot is ready; you now have 1 of them. == Minute 21 == Spend 3 ore and 14 clay to start building an obsidian-collecting robot. 2 ore-collecting robots collect 2 ore; you now have 2 ore. 7 clay-collecting robots collect 7 clay; you now have 7 clay. 4 obsidian-collecting robots collect 4 obsidian; you now have 11 obsidian. 1 geode-cracking robot cracks 1 geode; you now have 1 open geode. The new obsidian-collecting robot is ready; you now have 5 of them. == Minute 22 == Spend 2 ore and 7 obsidian to start building a geode-cracking robot. 2 ore-collecting robots collect 2 ore; you now have 2 ore. 7 clay-collecting robots collect 7 clay; you now have 14 clay. 5 obsidian-collecting robots collect 5 obsidian; you now have 9 obsidian. 1 geode-cracking robot cracks 1 geode; you now have 2 open geodes. The new geode-cracking robot is ready; you now have 2 of them. == Minute 23 == Spend 2 ore and 7 obsidian to start building a geode-cracking robot. 2 ore-collecting robots collect 2 ore; you now have 2 ore. 7 clay-collecting robots collect 7 clay; you now have 21 clay. 5 obsidian-collecting robots collect 5 obsidian; you now have 7 obsidian. 2 geode-cracking robots crack 2 geodes; you now have 4 open geodes. The new geode-cracking robot is ready; you now have 3 of them. == Minute 24 == Spend 2 ore and 7 obsidian to start building a geode-cracking robot. 2 ore-collecting robots collect 2 ore; you now have 2 ore. 7 clay-collecting robots collect 7 clay; you now have 28 clay. 5 obsidian-collecting robots collect 5 obsidian; you now have 5 obsidian. 3 geode-cracking robots crack 3 geodes; you now have 7 open geodes. The new geode-cracking robot is ready; you now have 4 of them. == Minute 25 == 2 ore-collecting robots collect 2 ore; you now have 4 ore. 7 clay-collecting robots collect 7 clay; you now have 35 clay. 5 obsidian-collecting robots collect 5 obsidian; you now have 10 obsidian. 4 geode-cracking robots crack 4 geodes; you now have 11 open geodes. == Minute 26 == Spend 2 ore and 7 obsidian to start building a geode-cracking robot. 2 ore-collecting robots collect 2 ore; you now have 4 ore. 7 clay-collecting robots collect 7 clay; you now have 42 clay. 5 obsidian-collecting robots collect 5 obsidian; you now have 8 obsidian. 4 geode-cracking robots crack 4 geodes; you now have 15 open geodes. The new geode-cracking robot is ready; you now have 5 of them. == Minute 27 == Spend 2 ore and 7 obsidian to start building a geode-cracking robot. 2 ore-collecting robots collect 2 ore; you now have 4 ore. 7 clay-collecting robots collect 7 clay; you now have 49 clay. 5 obsidian-collecting robots collect 5 obsidian; you now have 6 obsidian. 5 geode-cracking robots crack 5 geodes; you now have 20 open geodes. The new geode-cracking robot is ready; you now have 6 of them. == Minute 28 == 2 ore-collecting robots collect 2 ore; you now have 6 ore. 7 clay-collecting robots collect 7 clay; you now have 56 clay. 5 obsidian-collecting robots collect 5 obsidian; you now have 11 obsidian. 6 geode-cracking robots crack 6 geodes; you now have 26 open geodes. == Minute 29 == Spend 2 ore and 7 obsidian to start building a geode-cracking robot. 2 ore-collecting robots collect 2 ore; you now have 6 ore. 7 clay-collecting robots collect 7 clay; you now have 63 clay. 5 obsidian-collecting robots collect 5 obsidian; you now have 9 obsidian. 6 geode-cracking robots crack 6 geodes; you now have 32 open geodes. The new geode-cracking robot is ready; you now have 7 of them. == Minute 30 == Spend 2 ore and 7 obsidian to start building a geode-cracking robot. 2 ore-collecting robots collect 2 ore; you now have 6 ore. 7 clay-collecting robots collect 7 clay; you now have 70 clay. 5 obsidian-collecting robots collect 5 obsidian; you now have 7 obsidian. 7 geode-cracking robots crack 7 geodes; you now have 39 open geodes. The new geode-cracking robot is ready; you now have 8 of them. == Minute 31 == Spend 2 ore and 7 obsidian to start building a geode-cracking robot. 2 ore-collecting robots collect 2 ore; you now have 6 ore. 7 clay-collecting robots collect 7 clay; you now have 77 clay. 5 obsidian-collecting robots collect 5 obsidian; you now have 5 obsidian. 8 geode-cracking robots crack 8 geodes; you now have 47 open geodes. The new geode-cracking robot is ready; you now have 9 of them. == Minute 32 == 2 ore-collecting robots collect 2 ore; you now have 8 ore. 7 clay-collecting robots collect 7 clay; you now have 84 clay. 5 obsidian-collecting robots collect 5 obsidian; you now have 10 obsidian. 9 geode-cracking robots crack 9 geodes; you now have 56 open geodes. However, blueprint 2 from the example above is still better; using it, the largest number of geodes you could open in 32 minutes is 62. You no longer have enough blueprints to worry about quality levels. Instead, for each of the first three blueprints, determine the largest number of geodes you could open; then, multiply these three values together. Don't worry about quality levels; instead, just determine the largest number of geodes you could open using each of the first three blueprints. What do you get if you multiply these numbers together?	46
--- Day 19: A Series of Tubes --- Somehow, a network packet got lost and ended up here. It's trying to follow a routing diagram (your puzzle input), but it's confused about where to go. Its starting point is just off the top of the diagram. Lines (drawn with \|, -, and +) show the path it needs to take, starting by going down onto the only line connected to the top of the diagram. It needs to follow this path until it reaches the end (located somewhere within the diagram) and stop there. Sometimes, the lines cross over each other; in these cases, it needs to continue going the same direction, and only turn left or right when there's no other option. In addition, someone has left letters on the line; these also don't change its direction, but it can use them to keep track of where it's been. For example: \| \| +--+ A \| C F---\|----E\|--+ \| \| \| D +B-+ +--+ Given this diagram, the packet needs to take the following path: Starting at the only line touching the top of the diagram, it must go down, pass through A, and continue onward to the first +. Travel right, up, and right, passing through B in the process. Continue down (collecting C), right, and up (collecting D). Finally, go all the way left through E and stopping at F. Following the path to the end, the letters it sees on its path are ABCDEF. The little packet looks up at you, hoping you can help it find the way. What letters will it see (in the order it would see them) if it follows the path? (The routing diagram is very wide; make sure you view it without line wrapping.) Your puzzle answer was VTWBPYAQFU. --- Part Two --- The packet is curious how many steps it needs to go. For example, using the same routing diagram from the example above... \| \| +--+ A \| C F---\|--\|-E---+ \| \| \| D +B-+ +--+ ...the packet would go: 6 steps down (including the first line at the top of the diagram). 3 steps right. 4 steps up. 3 steps right. 4 steps down. 3 steps right. 2 steps up. 13 steps left (including the F it stops on). This would result in a total of 38 steps. How many steps does the packet need to go?	47
--- Day 22: Wizard Simulator 20XX --- Little Henry Case decides that defeating bosses with swords and stuff is boring. Now he's playing the game with a wizard. Of course, he gets stuck on another boss and needs your help again. In this version, combat still proceeds with the player and the boss taking alternating turns. The player still goes first. Now, however, you don't get any equipment; instead, you must choose one of your spells to cast. The first character at or below 0 hit points loses. Since you're a wizard, you don't get to wear armor, and you can't attack normally. However, since you do magic damage, your opponent's armor is ignored, and so the boss effectively has zero armor as well. As before, if armor (from a spell, in this case) would reduce damage below 1, it becomes 1 instead - that is, the boss' attacks always deal at least 1 damage. On each of your turns, you must select one of your spells to cast. If you cannot afford to cast any spell, you lose. Spells cost mana; you start with 500 mana, but have no maximum limit. You must have enough mana to cast a spell, and its cost is immediately deducted when you cast it. Your spells are Magic Missile, Drain, Shield, Poison, and Recharge. Magic Missile costs 53 mana. It instantly does 4 damage. Drain costs 73 mana. It instantly does 2 damage and heals you for 2 hit points. Shield costs 113 mana. It starts an effect that lasts for 6 turns. While it is active, your armor is increased by 7. Poison costs 173 mana. It starts an effect that lasts for 6 turns. At the start of each turn while it is active, it deals the boss 3 damage. Recharge costs 229 mana. It starts an effect that lasts for 5 turns. At the start of each turn while it is active, it gives you 101 new mana. Effects all work the same way. Effects apply at the start of both the player's turns and the boss' turns. Effects are created with a timer (the number of turns they last); at the start of each turn, after they apply any effect they have, their timer is decreased by one. If this decreases the timer to zero, the effect ends. You cannot cast a spell that would start an effect which is already active. However, effects can be started on the same turn they end. For example, suppose the player has 10 hit points and 250 mana, and that the boss has 13 hit points and 8 damage: -- Player turn -- - Player has 10 hit points, 0 armor, 250 mana - Boss has 13 hit points Player casts Poison. -- Boss turn -- - Player has 10 hit points, 0 armor, 77 mana - Boss has 13 hit points Poison deals 3 damage; its timer is now 5. Boss attacks for 8 damage. -- Player turn -- - Player has 2 hit points, 0 armor, 77 mana - Boss has 10 hit points Poison deals 3 damage; its timer is now 4. Player casts Magic Missile, dealing 4 damage. -- Boss turn -- - Player has 2 hit points, 0 armor, 24 mana - Boss has 3 hit points Poison deals 3 damage. This kills the boss, and the player wins. Now, suppose the same initial conditions, except that the boss has 14 hit points instead: -- Player turn -- - Player has 10 hit points, 0 armor, 250 mana - Boss has 14 hit points Player casts Recharge. -- Boss turn -- - Player has 10 hit points, 0 armor, 21 mana - Boss has 14 hit points Recharge provides 101 mana; its timer is now 4. Boss attacks for 8 damage! -- Player turn -- - Player has 2 hit points, 0 armor, 122 mana - Boss has 14 hit points Recharge provides 101 mana; its timer is now 3. Player casts Shield, increasing armor by 7. -- Boss turn -- - Player has 2 hit points, 7 armor, 110 mana - Boss has 14 hit points Shield's timer is now 5. Recharge provides 101 mana; its timer is now 2. Boss attacks for 8 - 7 = 1 damage! -- Player turn -- - Player has 1 hit point, 7 armor, 211 mana - Boss has 14 hit points Shield's timer is now 4. Recharge provides 101 mana; its timer is now 1. Player casts Drain, dealing 2 damage, and healing 2 hit points. -- Boss turn -- - Player has 3 hit points, 7 armor, 239 mana - Boss has 12 hit points Shield's timer is now 3. Recharge provides 101 mana; its timer is now 0. Recharge wears off. Boss attacks for 8 - 7 = 1 damage! -- Player turn -- - Player has 2 hit points, 7 armor, 340 mana - Boss has 12 hit points Shield's timer is now 2. Player casts Poison. -- Boss turn -- - Player has 2 hit points, 7 armor, 167 mana - Boss has 12 hit points Shield's timer is now 1. Poison deals 3 damage; its timer is now 5. Boss attacks for 8 - 7 = 1 damage! -- Player turn -- - Player has 1 hit point, 7 armor, 167 mana - Boss has 9 hit points Shield's timer is now 0. Shield wears off, decreasing armor by 7. Poison deals 3 damage; its timer is now 4. Player casts Magic Missile, dealing 4 damage. -- Boss turn -- - Player has 1 hit point, 0 armor, 114 mana - Boss has 2 hit points Poison deals 3 damage. This kills the boss, and the player wins. You start with 50 hit points and 500 mana points. The boss's actual stats are in your puzzle input. What is the least amount of mana you can spend and still win the fight? (Do not include mana recharge effects as "spending" negative mana.) Your puzzle answer was 953. --- Part Two --- On the next run through the game, you increase the difficulty to hard. At the start of each player turn (before any other effects apply), you lose 1 hit point. If this brings you to or below 0 hit points, you lose. With the same starting stats for you and the boss, what is the least amount of mana you can spend and still win the fight?	48
--- Day 18: Snailfish --- You descend into the ocean trench and encounter some snailfish. They say they saw the sleigh keys! They'll even tell you which direction the keys went if you help one of the smaller snailfish with his math homework. Snailfish numbers aren't like regular numbers. Instead, every snailfish number is a pair - an ordered list of two elements. Each element of the pair can be either a regular number or another pair. Pairs are written as [x,y], where x and y are the elements within the pair. Here are some example snailfish numbers, one snailfish number per line: [1,2] [[1,2],3] [9,[8,7]] [[1,9],[8,5]] [[[[1,2],[3,4]],[[5,6],[7,8]]],9] [[[9,[3,8]],[[0,9],6]],[[[3,7],[4,9]],3]] [[[[1,3],[5,3]],[[1,3],[8,7]]],[[[4,9],[6,9]],[[8,2],[7,3]]]] This snailfish homework is about addition. To add two snailfish numbers, form a pair from the left and right parameters of the addition operator. For example, [1,2] + [[3,4],5] becomes [[1,2],[[3,4],5]]. There's only one problem: snailfish numbers must always be reduced, and the process of adding two snailfish numbers can result in snailfish numbers that need to be reduced. To reduce a snailfish number, you must repeatedly do the first action in this list that applies to the snailfish number: If any pair is nested inside four pairs, the leftmost such pair explodes. If any regular number is 10 or greater, the leftmost such regular number splits. Once no action in the above list applies, the snailfish number is reduced. During reduction, at most one action applies, after which the process returns to the top of the list of actions. For example, if split produces a pair that meets the explode criteria, that pair explodes before other splits occur. To explode a pair, the pair's left value is added to the first regular number to the left of the exploding pair (if any), and the pair's right value is added to the first regular number to the right of the exploding pair (if any). Exploding pairs will always consist of two regular numbers. Then, the entire exploding pair is replaced with the regular number 0. Here are some examples of a single explode action: [[[[[9,8],1],2],3],4] becomes [[[[0,9],2],3],4] (the 9 has no regular number to its left, so it is not added to any regular number). [7,[6,[5,[4,[3,2]]]]] becomes [7,[6,[5,[7,0]]]] (the 2 has no regular number to its right, and so it is not added to any regular number). [[6,[5,[4,[3,2]]]],1] becomes [[6,[5,[7,0]]],3]. [[3,[2,[1,[7,3]]]],[6,[5,[4,[3,2]]]]] becomes [[3,[2,[8,0]]],[9,[5,[4,[3,2]]]]] (the pair [3,2] is unaffected because the pair [7,3] is further to the left; [3,2] would explode on the next action). [[3,[2,[8,0]]],[9,[5,[4,[3,2]]]]] becomes [[3,[2,[8,0]]],[9,[5,[7,0]]]]. To split a regular number, replace it with a pair; the left element of the pair should be the regular number divided by two and rounded down, while the right element of the pair should be the regular number divided by two and rounded up. For example, 10 becomes [5,5], 11 becomes [5,6], 12 becomes [6,6], and so on. Here is the process of finding the reduced result of [[[[4,3],4],4],[7,[[8,4],9]]] + [1,1]: after addition: [[[[[4,3],4],4],[7,[[8,4],9]]],[1,1]] after explode: [[[[0,7],4],[7,[[8,4],9]]],[1,1]] after explode: [[[[0,7],4],[15,[0,13]]],[1,1]] after split: [[[[0,7],4],[[7,8],[0,13]]],[1,1]] after split: [[[[0,7],4],[[7,8],[0,[6,7]]]],[1,1]] after explode: [[[[0,7],4],[[7,8],[6,0]]],[8,1]] Once no reduce actions apply, the snailfish number that remains is the actual result of the addition operation: [[[[0,7],4],[[7,8],[6,0]]],[8,1]]. The homework assignment involves adding up a list of snailfish numbers (your puzzle input). The snailfish numbers are each listed on a separate line. Add the first snailfish number and the second, then add that result and the third, then add that result and the fourth, and so on until all numbers in the list have been used once. For example, the final sum of this list is [[[[1,1],[2,2]],[3,3]],[4,4]]: [1,1] [2,2] [3,3] [4,4] The final sum of this list is [[[[3,0],[5,3]],[4,4]],[5,5]]: [1,1] [2,2] [3,3] [4,4] [5,5] The final sum of this list is [[[[5,0],[7,4]],[5,5]],[6,6]]: [1,1] [2,2] [3,3] [4,4] [5,5] [6,6] Here's a slightly larger example: [[[0,[4,5]],[0,0]],[[[4,5],[2,6]],[9,5]]] [7,[[[3,7],[4,3]],[[6,3],[8,8]]]] [[2,[[0,8],[3,4]]],[[[6,7],1],[7,[1,6]]]] [[[[2,4],7],[6,[0,5]]],[[[6,8],[2,8]],[[2,1],[4,5]]]] [7,[5,[[3,8],[1,4]]]] [[2,[2,2]],[8,[8,1]]] [2,9] [1,[[[9,3],9],[[9,0],[0,7]]]] [[[5,[7,4]],7],1] [[[[4,2],2],6],[8,7]] The final sum [[[[8,7],[7,7]],[[8,6],[7,7]]],[[[0,7],[6,6]],[8,7]]] is found after adding up the above snailfish numbers: [[[0,[4,5]],[0,0]],[[[4,5],[2,6]],[9,5]]] + [7,[[[3,7],[4,3]],[[6,3],[8,8]]]] = [[[[4,0],[5,4]],[[7,7],[6,0]]],[[8,[7,7]],[[7,9],[5,0]]]] [[[[4,0],[5,4]],[[7,7],[6,0]]],[[8,[7,7]],[[7,9],[5,0]]]] + [[2,[[0,8],[3,4]]],[[[6,7],1],[7,[1,6]]]] = [[[[6,7],[6,7]],[[7,7],[0,7]]],[[[8,7],[7,7]],[[8,8],[8,0]]]] [[[[6,7],[6,7]],[[7,7],[0,7]]],[[[8,7],[7,7]],[[8,8],[8,0]]]] + [[[[2,4],7],[6,[0,5]]],[[[6,8],[2,8]],[[2,1],[4,5]]]] = [[[[7,0],[7,7]],[[7,7],[7,8]]],[[[7,7],[8,8]],[[7,7],[8,7]]]] [[[[7,0],[7,7]],[[7,7],[7,8]]],[[[7,7],[8,8]],[[7,7],[8,7]]]] + [7,[5,[[3,8],[1,4]]]] = [[[[7,7],[7,8]],[[9,5],[8,7]]],[[[6,8],[0,8]],[[9,9],[9,0]]]] [[[[7,7],[7,8]],[[9,5],[8,7]]],[[[6,8],[0,8]],[[9,9],[9,0]]]] + [[2,[2,2]],[8,[8,1]]] = [[[[6,6],[6,6]],[[6,0],[6,7]]],[[[7,7],[8,9]],[8,[8,1]]]] [[[[6,6],[6,6]],[[6,0],[6,7]]],[[[7,7],[8,9]],[8,[8,1]]]] + [2,9] = [[[[6,6],[7,7]],[[0,7],[7,7]]],[[[5,5],[5,6]],9]] [[[[6,6],[7,7]],[[0,7],[7,7]]],[[[5,5],[5,6]],9]] + [1,[[[9,3],9],[[9,0],[0,7]]]] = [[[[7,8],[6,7]],[[6,8],[0,8]]],[[[7,7],[5,0]],[[5,5],[5,6]]]] [[[[7,8],[6,7]],[[6,8],[0,8]]],[[[7,7],[5,0]],[[5,5],[5,6]]]] + [[[5,[7,4]],7],1] = [[[[7,7],[7,7]],[[8,7],[8,7]]],[[[7,0],[7,7]],9]] [[[[7,7],[7,7]],[[8,7],[8,7]]],[[[7,0],[7,7]],9]] + [[[[4,2],2],6],[8,7]] = [[[[8,7],[7,7]],[[8,6],[7,7]]],[[[0,7],[6,6]],[8,7]]] To check whether it's the right answer, the snailfish teacher only checks the magnitude of the final sum. The magnitude of a pair is 3 times the magnitude of its left element plus 2 times the magnitude of its right element. The magnitude of a regular number is just that number. For example, the magnitude of [9,1] is 39 + 21 = 29; the magnitude of [1,9] is 31 + 29 = 21. Magnitude calculations are recursive: the magnitude of [[9,1],[1,9]] is 329 + 221 = 129. Here are a few more magnitude examples: [[1,2],[[3,4],5]] becomes 143. [[[[0,7],4],[[7,8],[6,0]]],[8,1]] becomes 1384. [[[[1,1],[2,2]],[3,3]],[4,4]] becomes 445. [[[[3,0],[5,3]],[4,4]],[5,5]] becomes 791. [[[[5,0],[7,4]],[5,5]],[6,6]] becomes 1137. [[[[8,7],[7,7]],[[8,6],[7,7]]],[[[0,7],[6,6]],[8,7]]] becomes 3488. So, given this example homework assignment: [[[0,[5,8]],[[1,7],[9,6]]],[[4,[1,2]],[[1,4],2]]] [[[5,[2,8]],4],[5,[[9,9],0]]] [6,[[[6,2],[5,6]],[[7,6],[4,7]]]] [[[6,[0,7]],[0,9]],[4,[9,[9,0]]]] [[[7,[6,4]],[3,[1,3]]],[[[5,5],1],9]] [[6,[[7,3],[3,2]]],[[[3,8],[5,7]],4]] [[[[5,4],[7,7]],8],[[8,3],8]] [[9,3],[[9,9],[6,[4,9]]]] [[2,[[7,7],7]],[[5,8],[[9,3],[0,2]]]] [[[[5,2],5],[8,[3,7]]],[[5,[7,5]],[4,4]]] The final sum is: [[[[6,6],[7,6]],[[7,7],[7,0]]],[[[7,7],[7,7]],[[7,8],[9,9]]]] The magnitude of this final sum is 4140. Add up all of the snailfish numbers from the homework assignment in the order they appear. What is the magnitude of the final sum? Your puzzle answer was 3486. --- Part Two --- You notice a second question on the back of the homework assignment: What is the largest magnitude you can get from adding only two of the snailfish numbers? Note that snailfish addition is not commutative - that is, x + y and y + x can produce different results. Again considering the last example homework assignment above: [[[0,[5,8]],[[1,7],[9,6]]],[[4,[1,2]],[[1,4],2]]] [[[5,[2,8]],4],[5,[[9,9],0]]] [6,[[[6,2],[5,6]],[[7,6],[4,7]]]] [[[6,[0,7]],[0,9]],[4,[9,[9,0]]]] [[[7,[6,4]],[3,[1,3]]],[[[5,5],1],9]] [[6,[[7,3],[3,2]]],[[[3,8],[5,7]],4]] [[[[5,4],[7,7]],8],[[8,3],8]] [[9,3],[[9,9],[6,[4,9]]]] [[2,[[7,7],7]],[[5,8],[[9,3],[0,2]]]] [[[[5,2],5],[8,[3,7]]],[[5,[7,5]],[4,4]]] The largest magnitude of the sum of any two snailfish numbers in this list is 3993. This is the magnitude of [[2,[[7,7],7]],[[5,8],[[9,3],[0,2]]]] + [[[0,[5,8]],[[1,7],[9,6]]],[[4,[1,2]],[[1,4],2]]], which reduces to [[[[7,8],[6,6]],[[6,0],[7,7]]],[[[7,8],[8,8]],[[7,9],[0,6]]]]. What is the largest magnitude of any sum of two different snailfish numbers from the homework assignment?	49
--- Day 14: Extended Polymerization --- The incredible pressures at this depth are starting to put a strain on your submarine. The submarine has polymerization equipment that would produce suitable materials to reinforce the submarine, and the nearby volcanically-active caves should even have the necessary input elements in sufficient quantities. The submarine manual contains instructions for finding the optimal polymer formula; specifically, it offers a polymer template and a list of pair insertion rules (your puzzle input). You just need to work out what polymer would result after repeating the pair insertion process a few times. For example: NNCB CH -> B HH -> N CB -> H NH -> C HB -> C HC -> B HN -> C NN -> C BH -> H NC -> B NB -> B BN -> B BB -> N BC -> B CC -> N CN -> C The first line is the polymer template - this is the starting point of the process. The following section defines the pair insertion rules. A rule like AB -> C means that when elements A and B are immediately adjacent, element C should be inserted between them. These insertions all happen simultaneously. So, starting with the polymer template NNCB, the first step simultaneously considers all three pairs: The first pair (NN) matches the rule NN -> C, so element C is inserted between the first N and the second N. The second pair (NC) matches the rule NC -> B, so element B is inserted between the N and the C. The third pair (CB) matches the rule CB -> H, so element H is inserted between the C and the B. Note that these pairs overlap: the second element of one pair is the first element of the next pair. Also, because all pairs are considered simultaneously, inserted elements are not considered to be part of a pair until the next step. After the first step of this process, the polymer becomes NCNBCHB. Here are the results of a few steps using the above rules: Template: NNCB After step 1: NCNBCHB After step 2: NBCCNBBBCBHCB After step 3: NBBBCNCCNBBNBNBBCHBHHBCHB After step 4: NBBNBNBBCCNBCNCCNBBNBBNBBBNBBNBBCBHCBHHNHCBBCBHCB This polymer grows quickly. After step 5, it has length 97; After step 10, it has length 3073. After step 10, B occurs 1749 times, C occurs 298 times, H occurs 161 times, and N occurs 865 times; taking the quantity of the most common element (B, 1749) and subtracting the quantity of the least common element (H, 161) produces 1749 - 161 = 1588. Apply 10 steps of pair insertion to the polymer template and find the most and least common elements in the result. What do you get if you take the quantity of the most common element and subtract the quantity of the least common element?	50
--- Day 8: Haunted Wasteland --- You're still riding a camel across Desert Island when you spot a sandstorm quickly approaching. When you turn to warn the Elf, she disappears before your eyes! To be fair, she had just finished warning you about ghosts a few minutes ago. One of the camel's pouches is labeled "maps" - sure enough, it's full of documents (your puzzle input) about how to navigate the desert. At least, you're pretty sure that's what they are; one of the documents contains a list of left/right instructions, and the rest of the documents seem to describe some kind of network of labeled nodes. It seems like you're meant to use the left/right instructions to navigate the network. Perhaps if you have the camel follow the same instructions, you can escape the haunted wasteland! After examining the maps for a bit, two nodes stick out: AAA and ZZZ. You feel like AAA is where you are now, and you have to follow the left/right instructions until you reach ZZZ. This format defines each node of the network individually. For example: RL AAA = (BBB, CCC) BBB = (DDD, EEE) CCC = (ZZZ, GGG) DDD = (DDD, DDD) EEE = (EEE, EEE) GGG = (GGG, GGG) ZZZ = (ZZZ, ZZZ) Starting with AAA, you need to look up the next element based on the next left/right instruction in your input. In this example, start with AAA and go right (R) by choosing the right element of AAA, CCC. Then, L means to choose the left element of CCC, ZZZ. By following the left/right instructions, you reach ZZZ in 2 steps. Of course, you might not find ZZZ right away. If you run out of left/right instructions, repeat the whole sequence of instructions as necessary: RL really means RLRLRLRLRLRLRLRL... and so on. For example, here is a situation that takes 6 steps to reach ZZZ: LLR AAA = (BBB, BBB) BBB = (AAA, ZZZ) ZZZ = (ZZZ, ZZZ) Starting at AAA, follow the left/right instructions. How many steps are required to reach ZZZ? Your puzzle answer was 12643. --- Part Two --- The sandstorm is upon you and you aren't any closer to escaping the wasteland. You had the camel follow the instructions, but you've barely left your starting position. It's going to take significantly more steps to escape! What if the map isn't for people - what if the map is for ghosts? Are ghosts even bound by the laws of spacetime? Only one way to find out. After examining the maps a bit longer, your attention is drawn to a curious fact: the number of nodes with names ending in A is equal to the number ending in Z! If you were a ghost, you'd probably just start at every node that ends with A and follow all of the paths at the same time until they all simultaneously end up at nodes that end with Z. For example: LR 11A = (11B, XXX) 11B = (XXX, 11Z) 11Z = (11B, XXX) 22A = (22B, XXX) 22B = (22C, 22C) 22C = (22Z, 22Z) 22Z = (22B, 22B) XXX = (XXX, XXX) Here, there are two starting nodes, 11A and 22A (because they both end with A). As you follow each left/right instruction, use that instruction to simultaneously navigate away from both nodes you're currently on. Repeat this process until all of the nodes you're currently on end with Z. (If only some of the nodes you're on end with Z, they act like any other node and you continue as normal.) In this example, you would proceed as follows: Step 0: You are at 11A and 22A. Step 1: You choose all of the left paths, leading you to 11B and 22B. Step 2: You choose all of the right paths, leading you to 11Z and 22C. Step 3: You choose all of the left paths, leading you to 11B and 22Z. Step 4: You choose all of the right paths, leading you to 11Z and 22B. Step 5: You choose all of the left paths, leading you to 11B and 22C. Step 6: You choose all of the right paths, leading you to 11Z and 22Z. So, in this example, you end up entirely on nodes that end in Z after 6 steps. Simultaneously start on every node that ends with A. How many steps does it take before you're only on nodes that end with Z?	51
--- Day 21: Dirac Dice --- There's not much to do as you slowly descend to the bottom of the ocean. The submarine computer challenges you to a nice game of Dirac Dice. This game consists of a single die, two pawns, and a game board with a circular track containing ten spaces marked 1 through 10 clockwise. Each player's starting space is chosen randomly (your puzzle input). Player 1 goes first. Players take turns moving. On each player's turn, the player rolls the die three times and adds up the results. Then, the player moves their pawn that many times forward around the track (that is, moving clockwise on spaces in order of increasing value, wrapping back around to 1 after 10). So, if a player is on space 7 and they roll 2, 2, and 1, they would move forward 5 times, to spaces 8, 9, 10, 1, and finally stopping on 2. After each player moves, they increase their score by the value of the space their pawn stopped on. Players' scores start at 0. So, if the first player starts on space 7 and rolls a total of 5, they would stop on space 2 and add 2 to their score (for a total score of 2). The game immediately ends as a win for any player whose score reaches at least 1000. Since the first game is a practice game, the submarine opens a compartment labeled deterministic dice and a 100-sided die falls out. This die always rolls 1 first, then 2, then 3, and so on up to 100, after which it starts over at 1 again. Play using this die. For example, given these starting positions: Player 1 starting position: 4 Player 2 starting position: 8 This is how the game would go: Player 1 rolls 1+2+3 and moves to space 10 for a total score of 10. Player 2 rolls 4+5+6 and moves to space 3 for a total score of 3. Player 1 rolls 7+8+9 and moves to space 4 for a total score of 14. Player 2 rolls 10+11+12 and moves to space 6 for a total score of 9. Player 1 rolls 13+14+15 and moves to space 6 for a total score of 20. Player 2 rolls 16+17+18 and moves to space 7 for a total score of 16. Player 1 rolls 19+20+21 and moves to space 6 for a total score of 26. Player 2 rolls 22+23+24 and moves to space 6 for a total score of 22. ...after many turns... Player 2 rolls 82+83+84 and moves to space 6 for a total score of 742. Player 1 rolls 85+86+87 and moves to space 4 for a total score of 990. Player 2 rolls 88+89+90 and moves to space 3 for a total score of 745. Player 1 rolls 91+92+93 and moves to space 10 for a final score, 1000. Since player 1 has at least 1000 points, player 1 wins and the game ends. At this point, the losing player had 745 points and the die had been rolled a total of 993 times; 745 * 993 = 739785. Play a practice game using the deterministic 100-sided die. The moment either player wins, what do you get if you multiply the score of the losing player by the number of times the die was rolled during the game?	52
--- Day 23: Safe Cracking --- This is one of the top floors of the nicest tower in EBHQ. The Easter Bunny's private office is here, complete with a safe hidden behind a painting, and who wouldn't hide a star in a safe behind a painting? The safe has a digital screen and keypad for code entry. A sticky note attached to the safe has a password hint on it: "eggs". The painting is of a large rabbit coloring some eggs. You see 7. When you go to type the code, though, nothing appears on the display; instead, the keypad comes apart in your hands, apparently having been smashed. Behind it is some kind of socket - one that matches a connector in your prototype computer! You pull apart the smashed keypad and extract the logic circuit, plug it into your computer, and plug your computer into the safe. Now, you just need to figure out what output the keypad would have sent to the safe. You extract the assembunny code from the logic chip (your puzzle input). The code looks like it uses almost the same architecture and instruction set that the monorail computer used! You should be able to use the same assembunny interpreter for this as you did there, but with one new instruction: tgl x toggles the instruction x away (pointing at instructions like jnz does: positive means forward; negative means backward): For one-argument instructions, inc becomes dec, and all other one-argument instructions become inc. For two-argument instructions, jnz becomes cpy, and all other two-instructions become jnz. The arguments of a toggled instruction are not affected. If an attempt is made to toggle an instruction outside the program, nothing happens. If toggling produces an invalid instruction (like cpy 1 2) and an attempt is later made to execute that instruction, skip it instead. If tgl toggles itself (for example, if a is 0, tgl a would target itself and become inc a), the resulting instruction is not executed until the next time it is reached. For example, given this program: cpy 2 a tgl a tgl a tgl a cpy 1 a dec a dec a cpy 2 a initializes register a to 2. The first tgl a toggles an instruction a (2) away from it, which changes the third tgl a into inc a. The second tgl a also modifies an instruction 2 away from it, which changes the cpy 1 a into jnz 1 a. The fourth line, which is now inc a, increments a to 3. Finally, the fifth line, which is now jnz 1 a, jumps a (3) instructions ahead, skipping the dec a instructions. In this example, the final value in register a is 3. The rest of the electronics seem to place the keypad entry (the number of eggs, 7) in register a, run the code, and then send the value left in register a to the safe. What value should be sent to the safe? Your puzzle answer was 12516. --- Part Two --- The safe doesn't open, but it does make several angry noises to express its frustration. You're quite sure your logic is working correctly, so the only other thing is... you check the painting again. As it turns out, colored eggs are still eggs. Now you count 12. As you run the program with this new input, the prototype computer begins to overheat. You wonder what's taking so long, and whether the lack of any instruction more powerful than "add one" has anything to do with it. Don't bunnies usually multiply? Anyway, what value should actually be sent to the safe?	53
--- Day 6: Wait For It --- The ferry quickly brings you across Island Island. After asking around, you discover that there is indeed normally a large pile of sand somewhere near here, but you don't see anything besides lots of water and the small island where the ferry has docked. As you try to figure out what to do next, you notice a poster on a wall near the ferry dock. "Boat races! Open to the public! Grand prize is an all-expenses-paid trip to Desert Island!" That must be where the sand comes from! Best of all, the boat races are starting in just a few minutes. You manage to sign up as a competitor in the boat races just in time. The organizer explains that it's not really a traditional race - instead, you will get a fixed amount of time during which your boat has to travel as far as it can, and you win if your boat goes the farthest. As part of signing up, you get a sheet of paper (your puzzle input) that lists the time allowed for each race and also the best distance ever recorded in that race. To guarantee you win the grand prize, you need to make sure you go farther in each race than the current record holder. The organizer brings you over to the area where the boat races are held. The boats are much smaller than you expected - they're actually toy boats, each with a big button on top. Holding down the button charges the boat, and releasing the button allows the boat to move. Boats move faster if their button was held longer, but time spent holding the button counts against the total race time. You can only hold the button at the start of the race, and boats don't move until the button is released. For example: Time: 7 15 30 Distance: 9 40 200 This document describes three races: The first race lasts 7 milliseconds. The record distance in this race is 9 millimeters. The second race lasts 15 milliseconds. The record distance in this race is 40 millimeters. The third race lasts 30 milliseconds. The record distance in this race is 200 millimeters. Your toy boat has a starting speed of zero millimeters per millisecond. For each whole millisecond you spend at the beginning of the race holding down the button, the boat's speed increases by one millimeter per millisecond. So, because the first race lasts 7 milliseconds, you only have a few options: Don't hold the button at all (that is, hold it for 0 milliseconds) at the start of the race. The boat won't move; it will have traveled 0 millimeters by the end of the race. Hold the button for 1 millisecond at the start of the race. Then, the boat will travel at a speed of 1 millimeter per millisecond for 6 milliseconds, reaching a total distance traveled of 6 millimeters. Hold the button for 2 milliseconds, giving the boat a speed of 2 millimeters per millisecond. It will then get 5 milliseconds to move, reaching a total distance of 10 millimeters. Hold the button for 3 milliseconds. After its remaining 4 milliseconds of travel time, the boat will have gone 12 millimeters. Hold the button for 4 milliseconds. After its remaining 3 milliseconds of travel time, the boat will have gone 12 millimeters. Hold the button for 5 milliseconds, causing the boat to travel a total of 10 millimeters. Hold the button for 6 milliseconds, causing the boat to travel a total of 6 millimeters. Hold the button for 7 milliseconds. That's the entire duration of the race. You never let go of the button. The boat can't move until you let go of the button. Please make sure you let go of the button so the boat gets to move. 0 millimeters. Since the current record for this race is 9 millimeters, there are actually 4 different ways you could win: you could hold the button for 2, 3, 4, or 5 milliseconds at the start of the race. In the second race, you could hold the button for at least 4 milliseconds and at most 11 milliseconds and beat the record, a total of 8 different ways to win. In the third race, you could hold the button for at least 11 milliseconds and no more than 19 milliseconds and still beat the record, a total of 9 ways you could win. To see how much margin of error you have, determine the number of ways you can beat the record in each race; in this example, if you multiply these values together, you get 288 (4 * 8 * 9). Determine the number of ways you could beat the record in each race. What do you get if you multiply these numbers together? Your puzzle answer was 74698. --- Part Two --- As the race is about to start, you realize the piece of paper with race times and record distances you got earlier actually just has very bad kerning. There's really only one race - ignore the spaces between the numbers on each line. So, the example from before: Time: 7 15 30 Distance: 9 40 200 ...now instead means this: Time: 71530 Distance: 940200 Now, you have to figure out how many ways there are to win this single race. In this example, the race lasts for 71530 milliseconds and the record distance you need to beat is 940200 millimeters. You could hold the button anywhere from 14 to 71516 milliseconds and beat the record, a total of 71503 ways! How many ways can you beat the record in this one much longer race?	54
--- Day 24: Crossed Wires --- You and The Historians arrive at the edge of a large grove somewhere in the jungle. After the last incident, the Elves installed a small device that monitors the fruit. While The Historians search the grove, one of them asks if you can take a look at the monitoring device; apparently, it's been malfunctioning recently. The device seems to be trying to produce a number through some boolean logic gates. Each gate has two inputs and one output. The gates all operate on values that are either true (1) or false (0). AND gates output 1 if both inputs are 1; if either input is 0, these gates output 0. OR gates output 1 if one or both inputs is 1; if both inputs are 0, these gates output 0. XOR gates output 1 if the inputs are different; if the inputs are the same, these gates output 0. Gates wait until both inputs are received before producing output; wires can carry 0, 1 or no value at all. There are no loops; once a gate has determined its output, the output will not change until the whole system is reset. Each wire is connected to at most one gate output, but can be connected to many gate inputs. Rather than risk getting shocked while tinkering with the live system, you write down all of the gate connections and initial wire values (your puzzle input) so you can consider them in relative safety. For example: x00: 1 x01: 1 x02: 1 y00: 0 y01: 1 y02: 0 x00 AND y00 -> z00 x01 XOR y01 -> z01 x02 OR y02 -> z02 Because gates wait for input, some wires need to start with a value (as inputs to the entire system). The first section specifies these values. For example, x00: 1 means that the wire named x00 starts with the value 1 (as if a gate is already outputting that value onto that wire). The second section lists all of the gates and the wires connected to them. For example, x00 AND y00 -> z00 describes an instance of an AND gate which has wires x00 and y00 connected to its inputs and which will write its output to wire z00. In this example, simulating these gates eventually causes 0 to appear on wire z00, 0 to appear on wire z01, and 1 to appear on wire z02. Ultimately, the system is trying to produce a number by combining the bits on all wires starting with z. z00 is the least significant bit, then z01, then z02, and so on. In this example, the three output bits form the binary number 100 which is equal to the decimal number 4. Here's a larger example: x00: 1 x01: 0 x02: 1 x03: 1 x04: 0 y00: 1 y01: 1 y02: 1 y03: 1 y04: 1 ntg XOR fgs -> mjb y02 OR x01 -> tnw kwq OR kpj -> z05 x00 OR x03 -> fst tgd XOR rvg -> z01 vdt OR tnw -> bfw bfw AND frj -> z10 ffh OR nrd -> bqk y00 AND y03 -> djm y03 OR y00 -> psh bqk OR frj -> z08 tnw OR fst -> frj gnj AND tgd -> z11 bfw XOR mjb -> z00 x03 OR x00 -> vdt gnj AND wpb -> z02 x04 AND y00 -> kjc djm OR pbm -> qhw nrd AND vdt -> hwm kjc AND fst -> rvg y04 OR y02 -> fgs y01 AND x02 -> pbm ntg OR kjc -> kwq psh XOR fgs -> tgd qhw XOR tgd -> z09 pbm OR djm -> kpj x03 XOR y03 -> ffh x00 XOR y04 -> ntg bfw OR bqk -> z06 nrd XOR fgs -> wpb frj XOR qhw -> z04 bqk OR frj -> z07 y03 OR x01 -> nrd hwm AND bqk -> z03 tgd XOR rvg -> z12 tnw OR pbm -> gnj After waiting for values on all wires starting with z, the wires in this system have the following values: bfw: 1 bqk: 1 djm: 1 ffh: 0 fgs: 1 frj: 1 fst: 1 gnj: 1 hwm: 1 kjc: 0 kpj: 1 kwq: 0 mjb: 1 nrd: 1 ntg: 0 pbm: 1 psh: 1 qhw: 1 rvg: 0 tgd: 0 tnw: 1 vdt: 1 wpb: 0 z00: 0 z01: 0 z02: 0 z03: 1 z04: 0 z05: 1 z06: 1 z07: 1 z08: 1 z09: 1 z10: 1 z11: 0 z12: 0 Combining the bits from all wires starting with z produces the binary number 0011111101000. Converting this number to decimal produces 2024. Simulate the system of gates and wires. What decimal number does it output on the wires starting with z? Your puzzle answer was 46362252142374. The first half of this puzzle is complete! It provides one gold star: * --- Part Two --- After inspecting the monitoring device more closely, you determine that the system you're simulating is trying to add two binary numbers. Specifically, it is treating the bits on wires starting with x as one binary number, treating the bits on wires starting with y as a second binary number, and then attempting to add those two numbers together. The output of this operation is produced as a binary number on the wires starting with z. (In all three cases, wire 00 is the least significant bit, then 01, then 02, and so on.) The initial values for the wires in your puzzle input represent just one instance of a pair of numbers that sum to the wrong value. Ultimately, any two binary numbers provided as input should be handled correctly. That is, for any combination of bits on wires starting with x and wires starting with y, the sum of the two numbers those bits represent should be produced as a binary number on the wires starting with z. For example, if you have an addition system with four x wires, four y wires, and five z wires, you should be able to supply any four-bit number on the x wires, any four-bit number on the y numbers, and eventually find the sum of those two numbers as a five-bit number on the z wires. One of the many ways you could provide numbers to such a system would be to pass 11 on the x wires (1011 in binary) and 13 on the y wires (1101 in binary): x00: 1 x01: 1 x02: 0 x03: 1 y00: 1 y01: 0 y02: 1 y03: 1 If the system were working correctly, then after all gates are finished processing, you should find 24 (11+13) on the z wires as the five-bit binary number 11000: z00: 0 z01: 0 z02: 0 z03: 1 z04: 1 Unfortunately, your actual system needs to add numbers with many more bits and therefore has many more wires. Based on forensic analysis of scuff marks and scratches on the device, you can tell that there are exactly four pairs of gates whose output wires have been swapped. (A gate can only be in at most one such pair; no gate's output was swapped multiple times.) For example, the system below is supposed to find the bitwise AND of the six-bit number on x00 through x05 and the six-bit number on y00 through y05 and then write the result as a six-bit number on z00 through z05: x00: 0 x01: 1 x02: 0 x03: 1 x04: 0 x05: 1 y00: 0 y01: 0 y02: 1 y03: 1 y04: 0 y05: 1 x00 AND y00 -> z05 x01 AND y01 -> z02 x02 AND y02 -> z01 x03 AND y03 -> z03 x04 AND y04 -> z04 x05 AND y05 -> z00 However, in this example, two pairs of gates have had their output wires swapped, causing the system to produce wrong answers. The first pair of gates with swapped outputs is x00 AND y00 -> z05 and x05 AND y05 -> z00; the second pair of gates is x01 AND y01 -> z02 and x02 AND y02 -> z01. Correcting these two swaps results in this system that works as intended for any set of initial values on wires that start with x or y: x00 AND y00 -> z00 x01 AND y01 -> z01 x02 AND y02 -> z02 x03 AND y03 -> z03 x04 AND y04 -> z04 x05 AND y05 -> z05 In this example, two pairs of gates have outputs that are involved in a swap. By sorting their output wires' names and joining them with commas, the list of wires involved in swaps is z00,z01,z02,z05. Of course, your actual system is much more complex than this, and the gates that need their outputs swapped could be anywhere, not just attached to a wire starting with z. If you were to determine that you need to swap output wires aaa with eee, ooo with z99, bbb with ccc, and aoc with z24, your answer would be aaa,aoc,bbb,ccc,eee,ooo,z24,z99. Your system of gates and wires has four pairs of gates which need their output wires swapped - eight wires in total. Determine which four pairs of gates need their outputs swapped so that your system correctly performs addition; what do you get if you sort the names of the eight wires involved in a swap and then join those names with commas?	55
--- Day 3: No Matter How You Slice It --- The Elves managed to locate the chimney-squeeze prototype fabric for Santa's suit (thanks to someone who helpfully wrote its box IDs on the wall of the warehouse in the middle of the night). Unfortunately, anomalies are still affecting them - nobody can even agree on how to cut the fabric. The whole piece of fabric they're working on is a very large square - at least 1000 inches on each side. Each Elf has made a claim about which area of fabric would be ideal for Santa's suit. All claims have an ID and consist of a single rectangle with edges parallel to the edges of the fabric. Each claim's rectangle is defined as follows: The number of inches between the left edge of the fabric and the left edge of the rectangle. The number of inches between the top edge of the fabric and the top edge of the rectangle. The width of the rectangle in inches. The height of the rectangle in inches. A claim like #123 @ 3,2: 5x4 means that claim ID 123 specifies a rectangle 3 inches from the left edge, 2 inches from the top edge, 5 inches wide, and 4 inches tall. Visually, it claims the square inches of fabric represented by # (and ignores the square inches of fabric represented by .) in the diagram below: ........... ........... ...#####... ...#####... ...#####... ...#####... ........... ........... ........... The problem is that many of the claims overlap, causing two or more claims to cover part of the same areas. For example, consider the following claims: #1 @ 1,3: 4x4 #2 @ 3,1: 4x4 #3 @ 5,5: 2x2 Visually, these claim the following areas: ........ ...2222. ...2222. .11XX22. .11XX22. .111133. .111133. ........ The four square inches marked with X are claimed by both 1 and 2. (Claim 3, while adjacent to the others, does not overlap either of them.) If the Elves all proceed with their own plans, none of them will have enough fabric. How many square inches of fabric are within two or more claims? Your puzzle answer was 101196. --- Part Two --- Amidst the chaos, you notice that exactly one claim doesn't overlap by even a single square inch of fabric with any other claim. If you can somehow draw attention to it, maybe the Elves will be able to make Santa's suit after all! For example, in the claims above, only claim 3 is intact after all claims are made. What is the ID of the only claim that doesn't overlap?	56
--- Day 10: Adapter Array --- Patched into the aircraft's data port, you discover weather forecasts of a massive tropical storm. Before you can figure out whether it will impact your vacation plans, however, your device suddenly turns off! Its battery is dead. You'll need to plug it in. There's only one problem: the charging outlet near your seat produces the wrong number of jolts. Always prepared, you make a list of all of the joltage adapters in your bag. Each of your joltage adapters is rated for a specific output joltage (your puzzle input). Any given adapter can take an input 1, 2, or 3 jolts lower than its rating and still produce its rated output joltage. In addition, your device has a built-in joltage adapter rated for 3 jolts higher than the highest-rated adapter in your bag. (If your adapter list were 3, 9, and 6, your device's built-in adapter would be rated for 12 jolts.) Treat the charging outlet near your seat as having an effective joltage rating of 0. Since you have some time to kill, you might as well test all of your adapters. Wouldn't want to get to your resort and realize you can't even charge your device! If you use every adapter in your bag at once, what is the distribution of joltage differences between the charging outlet, the adapters, and your device? For example, suppose that in your bag, you have adapters with the following joltage ratings: 16 10 15 5 1 11 7 19 6 12 4 With these adapters, your device's built-in joltage adapter would be rated for 19 + 3 = 22 jolts, 3 higher than the highest-rated adapter. Because adapters can only connect to a source 1-3 jolts lower than its rating, in order to use every adapter, you'd need to choose them like this: The charging outlet has an effective rating of 0 jolts, so the only adapters that could connect to it directly would need to have a joltage rating of 1, 2, or 3 jolts. Of these, only one you have is an adapter rated 1 jolt (difference of 1). From your 1-jolt rated adapter, the only choice is your 4-jolt rated adapter (difference of 3). From the 4-jolt rated adapter, the adapters rated 5, 6, or 7 are valid choices. However, in order to not skip any adapters, you have to pick the adapter rated 5 jolts (difference of 1). Similarly, the next choices would need to be the adapter rated 6 and then the adapter rated 7 (with difference of 1 and 1). The only adapter that works with the 7-jolt rated adapter is the one rated 10 jolts (difference of 3). From 10, the choices are 11 or 12; choose 11 (difference of 1) and then 12 (difference of 1). After 12, only valid adapter has a rating of 15 (difference of 3), then 16 (difference of 1), then 19 (difference of 3). Finally, your device's built-in adapter is always 3 higher than the highest adapter, so its rating is 22 jolts (always a difference of 3). In this example, when using every adapter, there are 7 differences of 1 jolt and 5 differences of 3 jolts. Here is a larger example: 28 33 18 42 31 14 46 20 48 47 24 23 49 45 19 38 39 11 1 32 25 35 8 17 7 9 4 2 34 10 3 In this larger example, in a chain that uses all of the adapters, there are 22 differences of 1 jolt and 10 differences of 3 jolts. Find a chain that uses all of your adapters to connect the charging outlet to your device's built-in adapter and count the joltage differences between the charging outlet, the adapters, and your device. What is the number of 1-jolt differences multiplied by the number of 3-jolt differences?	57
--- Day 1: Sonar Sweep --- You're minding your own business on a ship at sea when the overboard alarm goes off! You rush to see if you can help. Apparently, one of the Elves tripped and accidentally sent the sleigh keys flying into the ocean! Before you know it, you're inside a submarine the Elves keep ready for situations like this. It's covered in Christmas lights (because of course it is), and it even has an experimental antenna that should be able to track the keys if you can boost its signal strength high enough; there's a little meter that indicates the antenna's signal strength by displaying 0-50 stars. Your instincts tell you that in order to save Christmas, you'll need to get all fifty stars by December 25th. Collect stars by solving puzzles. Two puzzles will be made available on each day in the Advent calendar; the second puzzle is unlocked when you complete the first. Each puzzle grants one star. Good luck! As the submarine drops below the surface of the ocean, it automatically performs a sonar sweep of the nearby sea floor. On a small screen, the sonar sweep report (your puzzle input) appears: each line is a measurement of the sea floor depth as the sweep looks further and further away from the submarine. For example, suppose you had the following report: 199 200 208 210 200 207 240 269 260 263 This report indicates that, scanning outward from the submarine, the sonar sweep found depths of 199, 200, 208, 210, and so on. The first order of business is to figure out how quickly the depth increases, just so you know what you're dealing with - you never know if the keys will get carried into deeper water by an ocean current or a fish or something. To do this, count the number of times a depth measurement increases from the previous measurement. (There is no measurement before the first measurement.) In the example above, the changes are as follows: 199 (N/A - no previous measurement) 200 (increased) 208 (increased) 210 (increased) 200 (decreased) 207 (increased) 240 (increased) 269 (increased) 260 (decreased) 263 (increased) In this example, there are 7 measurements that are larger than the previous measurement. How many measurements are larger than the previous measurement? Your puzzle answer was 1766. --- Part Two --- Considering every single measurement isn't as useful as you expected: there's just too much noise in the data. Instead, consider sums of a three-measurement sliding window. Again considering the above example: 199 A 200 A B 208 A B C 210 B C D 200 E C D 207 E F D 240 E F G 269 F G H 260 G H 263 H Start by comparing the first and second three-measurement windows. The measurements in the first window are marked A (199, 200, 208); their sum is 199 + 200 + 208 = 607. The second window is marked B (200, 208, 210); its sum is 618. The sum of measurements in the second window is larger than the sum of the first, so this first comparison increased. Your goal now is to count the number of times the sum of measurements in this sliding window increases from the previous sum. So, compare A with B, then compare B with C, then C with D, and so on. Stop when there aren't enough measurements left to create a new three-measurement sum. In the above example, the sum of each three-measurement window is as follows: A: 607 (N/A - no previous sum) B: 618 (increased) C: 618 (no change) D: 617 (decreased) E: 647 (increased) F: 716 (increased) G: 769 (increased) H: 792 (increased) In this example, there are 5 sums that are larger than the previous sum. Consider sums of a three-measurement sliding window. How many sums are larger than the previous sum?	58
--- Day 2: I Was Told There Would Be No Math --- The elves are running low on wrapping paper, and so they need to submit an order for more. They have a list of the dimensions (length l, width w, and height h) of each present, and only want to order exactly as much as they need. Fortunately, every present is a box (a perfect right rectangular prism), which makes calculating the required wrapping paper for each gift a little easier: find the surface area of the box, which is 2lw + 2wh + 2hl. The elves also need a little extra paper for each present: the area of the smallest side. For example: A present with dimensions 2x3x4 requires 26 + 212 + 28 = 52 square feet of wrapping paper plus 6 square feet of slack, for a total of 58 square feet. A present with dimensions 1x1x10 requires 21 + 210 + 210 = 42 square feet of wrapping paper plus 1 square foot of slack, for a total of 43 square feet. All numbers in the elves' list are in feet. How many total square feet of wrapping paper should they order? Your puzzle answer was 1588178. --- Part Two --- The elves are also running low on ribbon. Ribbon is all the same width, so they only have to worry about the length they need to order, which they would again like to be exact. The ribbon required to wrap a present is the shortest distance around its sides, or the smallest perimeter of any one face. Each present also requires a bow made out of ribbon as well; the feet of ribbon required for the perfect bow is equal to the cubic feet of volume of the present. Don't ask how they tie the bow, though; they'll never tell. For example: A present with dimensions 2x3x4 requires 2+2+3+3 = 10 feet of ribbon to wrap the present plus 234 = 24 feet of ribbon for the bow, for a total of 34 feet. A present with dimensions 1x1x10 requires 1+1+1+1 = 4 feet of ribbon to wrap the present plus 1110 = 10 feet of ribbon for the bow, for a total of 14 feet. How many total feet of ribbon should they order?	59
--- Day 15: Dueling Generators --- Here, you encounter a pair of dueling generators. The generators, called generator A and generator B, are trying to agree on a sequence of numbers. However, one of them is malfunctioning, and so the sequences don't always match. As they do this, a judge waits for each of them to generate its next value, compares the lowest 16 bits of both values, and keeps track of the number of times those parts of the values match. The generators both work on the same principle. To create its next value, a generator will take the previous value it produced, multiply it by a factor (generator A uses 16807; generator B uses 48271), and then keep the remainder of dividing that resulting product by 2147483647. That final remainder is the value it produces next. To calculate each generator's first value, it instead uses a specific starting value as its "previous value" (as listed in your puzzle input). For example, suppose that for starting values, generator A uses 65, while generator B uses 8921. Then, the first five pairs of generated values are: --Gen. A-- --Gen. B-- 1092455 430625591 1181022009 1233683848 245556042 1431495498 1744312007 137874439 1352636452 285222916 In binary, these pairs are (with generator A's value first in each pair): 00000000000100001010101101100111 00011001101010101101001100110111 01000110011001001111011100111001 01001001100010001000010110001000 00001110101000101110001101001010 01010101010100101110001101001010 01100111111110000001011011000111 00001000001101111100110000000111 01010000100111111001100000100100 00010001000000000010100000000100 Here, you can see that the lowest (here, rightmost) 16 bits of the third value match: 1110001101001010. Because of this one match, after processing these five pairs, the judge would have added only 1 to its total. To get a significant sample, the judge would like to consider 40 million pairs. (In the example above, the judge would eventually find a total of 588 pairs that match in their lowest 16 bits.) After 40 million pairs, what is the judge's final count?	60
--- Day 22: Reactor Reboot --- Operating at these extreme ocean depths has overloaded the submarine's reactor; it needs to be rebooted. The reactor core is made up of a large 3-dimensional grid made up entirely of cubes, one cube per integer 3-dimensional coordinate (x,y,z). Each cube can be either on or off; at the start of the reboot process, they are all off. (Could it be an old model of a reactor you've seen before?) To reboot the reactor, you just need to set all of the cubes to either on or off by following a list of reboot steps (your puzzle input). Each step specifies a cuboid (the set of all cubes that have coordinates which fall within ranges for x, y, and z) and whether to turn all of the cubes in that cuboid on or off. For example, given these reboot steps: on x=10..12,y=10..12,z=10..12 on x=11..13,y=11..13,z=11..13 off x=9..11,y=9..11,z=9..11 on x=10..10,y=10..10,z=10..10 The first step (on x=10..12,y=10..12,z=10..12) turns on a 3x3x3 cuboid consisting of 27 cubes: 10,10,10 10,10,11 10,10,12 10,11,10 10,11,11 10,11,12 10,12,10 10,12,11 10,12,12 11,10,10 11,10,11 11,10,12 11,11,10 11,11,11 11,11,12 11,12,10 11,12,11 11,12,12 12,10,10 12,10,11 12,10,12 12,11,10 12,11,11 12,11,12 12,12,10 12,12,11 12,12,12 The second step (on x=11..13,y=11..13,z=11..13) turns on a 3x3x3 cuboid that overlaps with the first. As a result, only 19 additional cubes turn on; the rest are already on from the previous step: 11,11,13 11,12,13 11,13,11 11,13,12 11,13,13 12,11,13 12,12,13 12,13,11 12,13,12 12,13,13 13,11,11 13,11,12 13,11,13 13,12,11 13,12,12 13,12,13 13,13,11 13,13,12 13,13,13 The third step (off x=9..11,y=9..11,z=9..11) turns off a 3x3x3 cuboid that overlaps partially with some cubes that are on, ultimately turning off 8 cubes: 10,10,10 10,10,11 10,11,10 10,11,11 11,10,10 11,10,11 11,11,10 11,11,11 The final step (on x=10..10,y=10..10,z=10..10) turns on a single cube, 10,10,10. After this last step, 39 cubes are on. The initialization procedure only uses cubes that have x, y, and z positions of at least -50 and at most 50. For now, ignore cubes outside this region. Here is a larger example: on x=-20..26,y=-36..17,z=-47..7 on x=-20..33,y=-21..23,z=-26..28 on x=-22..28,y=-29..23,z=-38..16 on x=-46..7,y=-6..46,z=-50..-1 on x=-49..1,y=-3..46,z=-24..28 on x=2..47,y=-22..22,z=-23..27 on x=-27..23,y=-28..26,z=-21..29 on x=-39..5,y=-6..47,z=-3..44 on x=-30..21,y=-8..43,z=-13..34 on x=-22..26,y=-27..20,z=-29..19 off x=-48..-32,y=26..41,z=-47..-37 on x=-12..35,y=6..50,z=-50..-2 off x=-48..-32,y=-32..-16,z=-15..-5 on x=-18..26,y=-33..15,z=-7..46 off x=-40..-22,y=-38..-28,z=23..41 on x=-16..35,y=-41..10,z=-47..6 off x=-32..-23,y=11..30,z=-14..3 on x=-49..-5,y=-3..45,z=-29..18 off x=18..30,y=-20..-8,z=-3..13 on x=-41..9,y=-7..43,z=-33..15 on x=-54112..-39298,y=-85059..-49293,z=-27449..7877 on x=967..23432,y=45373..81175,z=27513..53682 The last two steps are fully outside the initialization procedure area; all other steps are fully within it. After executing these steps in the initialization procedure region, 590784 cubes are on. Execute the reboot steps. Afterward, considering only cubes in the region x=-50..50,y=-50..50,z=-50..50, how many cubes are on? Your puzzle answer was 607573. --- Part Two --- Now that the initialization procedure is complete, you can reboot the reactor. Starting with all cubes off, run all of the reboot steps for all cubes in the reactor. Consider the following reboot steps: on x=-5..47,y=-31..22,z=-19..33 on x=-44..5,y=-27..21,z=-14..35 on x=-49..-1,y=-11..42,z=-10..38 on x=-20..34,y=-40..6,z=-44..1 off x=26..39,y=40..50,z=-2..11 on x=-41..5,y=-41..6,z=-36..8 off x=-43..-33,y=-45..-28,z=7..25 on x=-33..15,y=-32..19,z=-34..11 off x=35..47,y=-46..-34,z=-11..5 on x=-14..36,y=-6..44,z=-16..29 on x=-57795..-6158,y=29564..72030,z=20435..90618 on x=36731..105352,y=-21140..28532,z=16094..90401 on x=30999..107136,y=-53464..15513,z=8553..71215 on x=13528..83982,y=-99403..-27377,z=-24141..23996 on x=-72682..-12347,y=18159..111354,z=7391..80950 on x=-1060..80757,y=-65301..-20884,z=-103788..-16709 on x=-83015..-9461,y=-72160..-8347,z=-81239..-26856 on x=-52752..22273,y=-49450..9096,z=54442..119054 on x=-29982..40483,y=-108474..-28371,z=-24328..38471 on x=-4958..62750,y=40422..118853,z=-7672..65583 on x=55694..108686,y=-43367..46958,z=-26781..48729 on x=-98497..-18186,y=-63569..3412,z=1232..88485 on x=-726..56291,y=-62629..13224,z=18033..85226 on x=-110886..-34664,y=-81338..-8658,z=8914..63723 on x=-55829..24974,y=-16897..54165,z=-121762..-28058 on x=-65152..-11147,y=22489..91432,z=-58782..1780 on x=-120100..-32970,y=-46592..27473,z=-11695..61039 on x=-18631..37533,y=-124565..-50804,z=-35667..28308 on x=-57817..18248,y=49321..117703,z=5745..55881 on x=14781..98692,y=-1341..70827,z=15753..70151 on x=-34419..55919,y=-19626..40991,z=39015..114138 on x=-60785..11593,y=-56135..2999,z=-95368..-26915 on x=-32178..58085,y=17647..101866,z=-91405..-8878 on x=-53655..12091,y=50097..105568,z=-75335..-4862 on x=-111166..-40997,y=-71714..2688,z=5609..50954 on x=-16602..70118,y=-98693..-44401,z=5197..76897 on x=16383..101554,y=4615..83635,z=-44907..18747 off x=-95822..-15171,y=-19987..48940,z=10804..104439 on x=-89813..-14614,y=16069..88491,z=-3297..45228 on x=41075..99376,y=-20427..49978,z=-52012..13762 on x=-21330..50085,y=-17944..62733,z=-112280..-30197 on x=-16478..35915,y=36008..118594,z=-7885..47086 off x=-98156..-27851,y=-49952..43171,z=-99005..-8456 off x=2032..69770,y=-71013..4824,z=7471..94418 on x=43670..120875,y=-42068..12382,z=-24787..38892 off x=37514..111226,y=-45862..25743,z=-16714..54663 off x=25699..97951,y=-30668..59918,z=-15349..69697 off x=-44271..17935,y=-9516..60759,z=49131..112598 on x=-61695..-5813,y=40978..94975,z=8655..80240 off x=-101086..-9439,y=-7088..67543,z=33935..83858 off x=18020..114017,y=-48931..32606,z=21474..89843 off x=-77139..10506,y=-89994..-18797,z=-80..59318 off x=8476..79288,y=-75520..11602,z=-96624..-24783 on x=-47488..-1262,y=24338..100707,z=16292..72967 off x=-84341..13987,y=2429..92914,z=-90671..-1318 off x=-37810..49457,y=-71013..-7894,z=-105357..-13188 off x=-27365..46395,y=31009..98017,z=15428..76570 off x=-70369..-16548,y=22648..78696,z=-1892..86821 on x=-53470..21291,y=-120233..-33476,z=-44150..38147 off x=-93533..-4276,y=-16170..68771,z=-104985..-24507 After running the above reboot steps, 2758514936282235 cubes are on. (Just for fun, 474140 of those are also in the initialization procedure region.) Starting again with all cubes off, execute all reboot steps. Afterward, considering all cubes, how many cubes are on?	61
--- Day 21: Allergen Assessment --- You reach the train's last stop and the closest you can get to your vacation island without getting wet. There aren't even any boats here, but nothing can stop you now: you build a raft. You just need a few days' worth of food for your journey. You don't speak the local language, so you can't read any ingredients lists. However, sometimes, allergens are listed in a language you do understand. You should be able to use this information to determine which ingredient contains which allergen and work out which foods are safe to take with you on your trip. You start by compiling a list of foods (your puzzle input), one food per line. Each line includes that food's ingredients list followed by some or all of the allergens the food contains. Each allergen is found in exactly one ingredient. Each ingredient contains zero or one allergen. Allergens aren't always marked; when they're listed (as in (contains nuts, shellfish) after an ingredients list), the ingredient that contains each listed allergen will be somewhere in the corresponding ingredients list. However, even if an allergen isn't listed, the ingredient that contains that allergen could still be present: maybe they forgot to label it, or maybe it was labeled in a language you don't know. For example, consider the following list of foods: mxmxvkd kfcds sqjhc nhms (contains dairy, fish) trh fvjkl sbzzf mxmxvkd (contains dairy) sqjhc fvjkl (contains soy) sqjhc mxmxvkd sbzzf (contains fish) The first food in the list has four ingredients (written in a language you don't understand): mxmxvkd, kfcds, sqjhc, and nhms. While the food might contain other allergens, a few allergens the food definitely contains are listed afterward: dairy and fish. The first step is to determine which ingredients can't possibly contain any of the allergens in any food in your list. In the above example, none of the ingredients kfcds, nhms, sbzzf, or trh can contain an allergen. Counting the number of times any of these ingredients appear in any ingredients list produces 5: they all appear once each except sbzzf, which appears twice. Determine which ingredients cannot possibly contain any of the allergens in your list. How many times do any of those ingredients appear?	62
--- Day 24: Lobby Layout --- Your raft makes it to the tropical island; it turns out that the small crab was an excellent navigator. You make your way to the resort. As you enter the lobby, you discover a small problem: the floor is being renovated. You can't even reach the check-in desk until they've finished installing the new tile floor. The tiles are all hexagonal; they need to be arranged in a hex grid with a very specific color pattern. Not in the mood to wait, you offer to help figure out the pattern. The tiles are all white on one side and black on the other. They start with the white side facing up. The lobby is large enough to fit whatever pattern might need to appear there. A member of the renovation crew gives you a list of the tiles that need to be flipped over (your puzzle input). Each line in the list identifies a single tile that needs to be flipped by giving a series of steps starting from a reference tile in the very center of the room. (Every line starts from the same reference tile.) Because the tiles are hexagonal, every tile has six neighbors: east, southeast, southwest, west, northwest, and northeast. These directions are given in your list, respectively, as e, se, sw, w, nw, and ne. A tile is identified by a series of these directions with no delimiters; for example, esenee identifies the tile you land on if you start at the reference tile and then move one tile east, one tile southeast, one tile northeast, and one tile east. Each time a tile is identified, it flips from white to black or from black to white. Tiles might be flipped more than once. For example, a line like esew flips a tile immediately adjacent to the reference tile, and a line like nwwswee flips the reference tile itself. Here is a larger example: sesenwnenenewseeswwswswwnenewsewsw neeenesenwnwwswnenewnwwsewnenwseswesw seswneswswsenwwnwse nwnwneseeswswnenewneswwnewseswneseene swweswneswnenwsewnwneneseenw eesenwseswswnenwswnwnwsewwnwsene sewnenenenesenwsewnenwwwse wenwwweseeeweswwwnwwe wsweesenenewnwwnwsenewsenwwsesesenwne neeswseenwwswnwswswnw nenwswwsewswnenenewsenwsenwnesesenew enewnwewneswsewnwswenweswnenwsenwsw sweneswneswneneenwnewenewwneswswnese swwesenesewenwneswnwwneseswwne enesenwswwswneneswsenwnewswseenwsese wnwnesenesenenwwnenwsewesewsesesew nenewswnwewswnenesenwnesewesw eneswnwswnwsenenwnwnwwseeswneewsenese neswnwewnwnwseenwseesewsenwsweewe wseweeenwnesenwwwswnew In the above example, 10 tiles are flipped once (to black), and 5 more are flipped twice (to black, then back to white). After all of these instructions have been followed, a total of 10 tiles are black. Go through the renovation crew's list and determine which tiles they need to flip. After all of the instructions have been followed, how many tiles are left with the black side up?	63
--- Day 14: Chocolate Charts --- You finally have a chance to look at all of the produce moving around. Chocolate, cinnamon, mint, chili peppers, nutmeg, vanilla... the Elves must be growing these plants to make hot chocolate! As you realize this, you hear a conversation in the distance. When you go to investigate, you discover two Elves in what appears to be a makeshift underground kitchen/laboratory. The Elves are trying to come up with the ultimate hot chocolate recipe; they're even maintaining a scoreboard which tracks the quality score (0-9) of each recipe. Only two recipes are on the board: the first recipe got a score of 3, the second, 7. Each of the two Elves has a current recipe: the first Elf starts with the first recipe, and the second Elf starts with the second recipe. To create new recipes, the two Elves combine their current recipes. This creates new recipes from the digits of the sum of the current recipes' scores. With the current recipes' scores of 3 and 7, their sum is 10, and so two new recipes would be created: the first with score 1 and the second with score 0. If the current recipes' scores were 2 and 3, the sum, 5, would only create one recipe (with a score of 5) with its single digit. The new recipes are added to the end of the scoreboard in the order they are created. So, after the first round, the scoreboard is 3, 7, 1, 0. After all new recipes are added to the scoreboard, each Elf picks a new current recipe. To do this, the Elf steps forward through the scoreboard a number of recipes equal to 1 plus the score of their current recipe. So, after the first round, the first Elf moves forward 1 + 3 = 4 times, while the second Elf moves forward 1 + 7 = 8 times. If they run out of recipes, they loop back around to the beginning. After the first round, both Elves happen to loop around until they land on the same recipe that they had in the beginning; in general, they will move to different recipes. Drawing the first Elf as parentheses and the second Elf as square brackets, they continue this process: (3)[7] (3)[7] 1 0 3 7 1 [0](1) 0 3 7 1 0 [1] 0 (1) (3) 7 1 0 1 0 [1] 2 3 7 1 0 (1) 0 1 2 [4] 3 7 1 [0] 1 0 (1) 2 4 5 3 7 1 0 [1] 0 1 2 (4) 5 1 3 (7) 1 0 1 0 [1] 2 4 5 1 5 3 7 1 0 1 0 1 2 [4](5) 1 5 8 3 (7) 1 0 1 0 1 2 4 5 1 5 8 [9] 3 7 1 0 1 0 1 [2] 4 (5) 1 5 8 9 1 6 3 7 1 0 1 0 1 2 4 5 [1] 5 8 9 1 (6) 7 3 7 1 0 (1) 0 1 2 4 5 1 5 [8] 9 1 6 7 7 3 7 [1] 0 1 0 (1) 2 4 5 1 5 8 9 1 6 7 7 9 3 7 1 0 [1] 0 1 2 (4) 5 1 5 8 9 1 6 7 7 9 2 The Elves think their skill will improve after making a few recipes (your puzzle input). However, that could take ages; you can speed this up considerably by identifying the scores of the ten recipes after that. For example: If the Elves think their skill will improve after making 9 recipes, the scores of the ten recipes after the first nine on the scoreboard would be 5158916779 (highlighted in the last line of the diagram). After 5 recipes, the scores of the next ten would be 0124515891. After 18 recipes, the scores of the next ten would be 9251071085. After 2018 recipes, the scores of the next ten would be 5941429882. What are the scores of the ten recipes immediately after the number of recipes in your puzzle input? Your puzzle answer was 1413131339. --- Part Two --- As it turns out, you got the Elves' plan backwards. They actually want to know how many recipes appear on the scoreboard to the left of the first recipes whose scores are the digits from your puzzle input. 51589 first appears after 9 recipes. 01245 first appears after 5 recipes. 92510 first appears after 18 recipes. 59414 first appears after 2018 recipes. How many recipes appear on the scoreboard to the left of the score sequence in your puzzle input?	64
--- Day 22: Wizard Simulator 20XX --- Little Henry Case decides that defeating bosses with swords and stuff is boring. Now he's playing the game with a wizard. Of course, he gets stuck on another boss and needs your help again. In this version, combat still proceeds with the player and the boss taking alternating turns. The player still goes first. Now, however, you don't get any equipment; instead, you must choose one of your spells to cast. The first character at or below 0 hit points loses. Since you're a wizard, you don't get to wear armor, and you can't attack normally. However, since you do magic damage, your opponent's armor is ignored, and so the boss effectively has zero armor as well. As before, if armor (from a spell, in this case) would reduce damage below 1, it becomes 1 instead - that is, the boss' attacks always deal at least 1 damage. On each of your turns, you must select one of your spells to cast. If you cannot afford to cast any spell, you lose. Spells cost mana; you start with 500 mana, but have no maximum limit. You must have enough mana to cast a spell, and its cost is immediately deducted when you cast it. Your spells are Magic Missile, Drain, Shield, Poison, and Recharge. Magic Missile costs 53 mana. It instantly does 4 damage. Drain costs 73 mana. It instantly does 2 damage and heals you for 2 hit points. Shield costs 113 mana. It starts an effect that lasts for 6 turns. While it is active, your armor is increased by 7. Poison costs 173 mana. It starts an effect that lasts for 6 turns. At the start of each turn while it is active, it deals the boss 3 damage. Recharge costs 229 mana. It starts an effect that lasts for 5 turns. At the start of each turn while it is active, it gives you 101 new mana. Effects all work the same way. Effects apply at the start of both the player's turns and the boss' turns. Effects are created with a timer (the number of turns they last); at the start of each turn, after they apply any effect they have, their timer is decreased by one. If this decreases the timer to zero, the effect ends. You cannot cast a spell that would start an effect which is already active. However, effects can be started on the same turn they end. For example, suppose the player has 10 hit points and 250 mana, and that the boss has 13 hit points and 8 damage: -- Player turn -- - Player has 10 hit points, 0 armor, 250 mana - Boss has 13 hit points Player casts Poison. -- Boss turn -- - Player has 10 hit points, 0 armor, 77 mana - Boss has 13 hit points Poison deals 3 damage; its timer is now 5. Boss attacks for 8 damage. -- Player turn -- - Player has 2 hit points, 0 armor, 77 mana - Boss has 10 hit points Poison deals 3 damage; its timer is now 4. Player casts Magic Missile, dealing 4 damage. -- Boss turn -- - Player has 2 hit points, 0 armor, 24 mana - Boss has 3 hit points Poison deals 3 damage. This kills the boss, and the player wins. Now, suppose the same initial conditions, except that the boss has 14 hit points instead: -- Player turn -- - Player has 10 hit points, 0 armor, 250 mana - Boss has 14 hit points Player casts Recharge. -- Boss turn -- - Player has 10 hit points, 0 armor, 21 mana - Boss has 14 hit points Recharge provides 101 mana; its timer is now 4. Boss attacks for 8 damage! -- Player turn -- - Player has 2 hit points, 0 armor, 122 mana - Boss has 14 hit points Recharge provides 101 mana; its timer is now 3. Player casts Shield, increasing armor by 7. -- Boss turn -- - Player has 2 hit points, 7 armor, 110 mana - Boss has 14 hit points Shield's timer is now 5. Recharge provides 101 mana; its timer is now 2. Boss attacks for 8 - 7 = 1 damage! -- Player turn -- - Player has 1 hit point, 7 armor, 211 mana - Boss has 14 hit points Shield's timer is now 4. Recharge provides 101 mana; its timer is now 1. Player casts Drain, dealing 2 damage, and healing 2 hit points. -- Boss turn -- - Player has 3 hit points, 7 armor, 239 mana - Boss has 12 hit points Shield's timer is now 3. Recharge provides 101 mana; its timer is now 0. Recharge wears off. Boss attacks for 8 - 7 = 1 damage! -- Player turn -- - Player has 2 hit points, 7 armor, 340 mana - Boss has 12 hit points Shield's timer is now 2. Player casts Poison. -- Boss turn -- - Player has 2 hit points, 7 armor, 167 mana - Boss has 12 hit points Shield's timer is now 1. Poison deals 3 damage; its timer is now 5. Boss attacks for 8 - 7 = 1 damage! -- Player turn -- - Player has 1 hit point, 7 armor, 167 mana - Boss has 9 hit points Shield's timer is now 0. Shield wears off, decreasing armor by 7. Poison deals 3 damage; its timer is now 4. Player casts Magic Missile, dealing 4 damage. -- Boss turn -- - Player has 1 hit point, 0 armor, 114 mana - Boss has 2 hit points Poison deals 3 damage. This kills the boss, and the player wins. You start with 50 hit points and 500 mana points. The boss's actual stats are in your puzzle input. What is the least amount of mana you can spend and still win the fight? (Do not include mana recharge effects as "spending" negative mana.)	65
--- Day 7: Some Assembly Required --- This year, Santa brought little Bobby Tables a set of wires and bitwise logic gates! Unfortunately, little Bobby is a little under the recommended age range, and he needs help assembling the circuit. Each wire has an identifier (some lowercase letters) and can carry a 16-bit signal (a number from 0 to 65535). A signal is provided to each wire by a gate, another wire, or some specific value. Each wire can only get a signal from one source, but can provide its signal to multiple destinations. A gate provides no signal until all of its inputs have a signal. The included instructions booklet describes how to connect the parts together: x AND y -> z means to connect wires x and y to an AND gate, and then connect its output to wire z. For example: 123 -> x means that the signal 123 is provided to wire x. x AND y -> z means that the bitwise AND of wire x and wire y is provided to wire z. p LSHIFT 2 -> q means that the value from wire p is left-shifted by 2 and then provided to wire q. NOT e -> f means that the bitwise complement of the value from wire e is provided to wire f. Other possible gates include OR (bitwise OR) and RSHIFT (right-shift). If, for some reason, you'd like to emulate the circuit instead, almost all programming languages (for example, C, JavaScript, or Python) provide operators for these gates. For example, here is a simple circuit: 123 -> x 456 -> y x AND y -> d x OR y -> e x LSHIFT 2 -> f y RSHIFT 2 -> g NOT x -> h NOT y -> i After it is run, these are the signals on the wires: d: 72 e: 507 f: 492 g: 114 h: 65412 i: 65079 x: 123 y: 456 In little Bobby's kit's instructions booklet (provided as your puzzle input), what signal is ultimately provided to wire a? Your puzzle answer was 16076. --- Part Two --- Now, take the signal you got on wire a, override wire b to that signal, and reset the other wires (including wire a). What new signal is ultimately provided to wire a?	66
--- Day 11: Monkey in the Middle --- As you finally start making your way upriver, you realize your pack is much lighter than you remember. Just then, one of the items from your pack goes flying overhead. Monkeys are playing Keep Away with your missing things! To get your stuff back, you need to be able to predict where the monkeys will throw your items. After some careful observation, you realize the monkeys operate based on how worried you are about each item. You take some notes (your puzzle input) on the items each monkey currently has, how worried you are about those items, and how the monkey makes decisions based on your worry level. For example: Monkey 0: Starting items: 79, 98 Operation: new = old * 19 Test: divisible by 23 If true: throw to monkey 2 If false: throw to monkey 3 Monkey 1: Starting items: 54, 65, 75, 74 Operation: new = old + 6 Test: divisible by 19 If true: throw to monkey 2 If false: throw to monkey 0 Monkey 2: Starting items: 79, 60, 97 Operation: new = old * old Test: divisible by 13 If true: throw to monkey 1 If false: throw to monkey 3 Monkey 3: Starting items: 74 Operation: new = old + 3 Test: divisible by 17 If true: throw to monkey 0 If false: throw to monkey 1 Each monkey has several attributes: Starting items lists your worry level for each item the monkey is currently holding in the order they will be inspected. Operation shows how your worry level changes as that monkey inspects an item. (An operation like new = old * 5 means that your worry level after the monkey inspected the item is five times whatever your worry level was before inspection.) Test shows how the monkey uses your worry level to decide where to throw an item next. If true shows what happens with an item if the Test was true. If false shows what happens with an item if the Test was false. After each monkey inspects an item but before it tests your worry level, your relief that the monkey's inspection didn't damage the item causes your worry level to be divided by three and rounded down to the nearest integer. The monkeys take turns inspecting and throwing items. On a single monkey's turn, it inspects and throws all of the items it is holding one at a time and in the order listed. Monkey 0 goes first, then monkey 1, and so on until each monkey has had one turn. The process of each monkey taking a single turn is called a round. When a monkey throws an item to another monkey, the item goes on the end of the recipient monkey's list. A monkey that starts a round with no items could end up inspecting and throwing many items by the time its turn comes around. If a monkey is holding no items at the start of its turn, its turn ends. In the above example, the first round proceeds as follows: Monkey 0: Monkey inspects an item with a worry level of 79. Worry level is multiplied by 19 to 1501. Monkey gets bored with item. Worry level is divided by 3 to 500. Current worry level is not divisible by 23. Item with worry level 500 is thrown to monkey 3. Monkey inspects an item with a worry level of 98. Worry level is multiplied by 19 to 1862. Monkey gets bored with item. Worry level is divided by 3 to 620. Current worry level is not divisible by 23. Item with worry level 620 is thrown to monkey 3. Monkey 1: Monkey inspects an item with a worry level of 54. Worry level increases by 6 to 60. Monkey gets bored with item. Worry level is divided by 3 to 20. Current worry level is not divisible by 19. Item with worry level 20 is thrown to monkey 0. Monkey inspects an item with a worry level of 65. Worry level increases by 6 to 71. Monkey gets bored with item. Worry level is divided by 3 to 23. Current worry level is not divisible by 19. Item with worry level 23 is thrown to monkey 0. Monkey inspects an item with a worry level of 75. Worry level increases by 6 to 81. Monkey gets bored with item. Worry level is divided by 3 to 27. Current worry level is not divisible by 19. Item with worry level 27 is thrown to monkey 0. Monkey inspects an item with a worry level of 74. Worry level increases by 6 to 80. Monkey gets bored with item. Worry level is divided by 3 to 26. Current worry level is not divisible by 19. Item with worry level 26 is thrown to monkey 0. Monkey 2: Monkey inspects an item with a worry level of 79. Worry level is multiplied by itself to 6241. Monkey gets bored with item. Worry level is divided by 3 to 2080. Current worry level is divisible by 13. Item with worry level 2080 is thrown to monkey 1. Monkey inspects an item with a worry level of 60. Worry level is multiplied by itself to 3600. Monkey gets bored with item. Worry level is divided by 3 to 1200. Current worry level is not divisible by 13. Item with worry level 1200 is thrown to monkey 3. Monkey inspects an item with a worry level of 97. Worry level is multiplied by itself to 9409. Monkey gets bored with item. Worry level is divided by 3 to 3136. Current worry level is not divisible by 13. Item with worry level 3136 is thrown to monkey 3. Monkey 3: Monkey inspects an item with a worry level of 74. Worry level increases by 3 to 77. Monkey gets bored with item. Worry level is divided by 3 to 25. Current worry level is not divisible by 17. Item with worry level 25 is thrown to monkey 1. Monkey inspects an item with a worry level of 500. Worry level increases by 3 to 503. Monkey gets bored with item. Worry level is divided by 3 to 167. Current worry level is not divisible by 17. Item with worry level 167 is thrown to monkey 1. Monkey inspects an item with a worry level of 620. Worry level increases by 3 to 623. Monkey gets bored with item. Worry level is divided by 3 to 207. Current worry level is not divisible by 17. Item with worry level 207 is thrown to monkey 1. Monkey inspects an item with a worry level of 1200. Worry level increases by 3 to 1203. Monkey gets bored with item. Worry level is divided by 3 to 401. Current worry level is not divisible by 17. Item with worry level 401 is thrown to monkey 1. Monkey inspects an item with a worry level of 3136. Worry level increases by 3 to 3139. Monkey gets bored with item. Worry level is divided by 3 to 1046. Current worry level is not divisible by 17. Item with worry level 1046 is thrown to monkey 1. After round 1, the monkeys are holding items with these worry levels: Monkey 0: 20, 23, 27, 26 Monkey 1: 2080, 25, 167, 207, 401, 1046 Monkey 2: Monkey 3: Monkeys 2 and 3 aren't holding any items at the end of the round; they both inspected items during the round and threw them all before the round ended. This process continues for a few more rounds: After round 2, the monkeys are holding items with these worry levels: Monkey 0: 695, 10, 71, 135, 350 Monkey 1: 43, 49, 58, 55, 362 Monkey 2: Monkey 3: After round 3, the monkeys are holding items with these worry levels: Monkey 0: 16, 18, 21, 20, 122 Monkey 1: 1468, 22, 150, 286, 739 Monkey 2: Monkey 3: After round 4, the monkeys are holding items with these worry levels: Monkey 0: 491, 9, 52, 97, 248, 34 Monkey 1: 39, 45, 43, 258 Monkey 2: Monkey 3: After round 5, the monkeys are holding items with these worry levels: Monkey 0: 15, 17, 16, 88, 1037 Monkey 1: 20, 110, 205, 524, 72 Monkey 2: Monkey 3: After round 6, the monkeys are holding items with these worry levels: Monkey 0: 8, 70, 176, 26, 34 Monkey 1: 481, 32, 36, 186, 2190 Monkey 2: Monkey 3: After round 7, the monkeys are holding items with these worry levels: Monkey 0: 162, 12, 14, 64, 732, 17 Monkey 1: 148, 372, 55, 72 Monkey 2: Monkey 3: After round 8, the monkeys are holding items with these worry levels: Monkey 0: 51, 126, 20, 26, 136 Monkey 1: 343, 26, 30, 1546, 36 Monkey 2: Monkey 3: After round 9, the monkeys are holding items with these worry levels: Monkey 0: 116, 10, 12, 517, 14 Monkey 1: 108, 267, 43, 55, 288 Monkey 2: Monkey 3: After round 10, the monkeys are holding items with these worry levels: Monkey 0: 91, 16, 20, 98 Monkey 1: 481, 245, 22, 26, 1092, 30 Monkey 2: Monkey 3: ... After round 15, the monkeys are holding items with these worry levels: Monkey 0: 83, 44, 8, 184, 9, 20, 26, 102 Monkey 1: 110, 36 Monkey 2: Monkey 3: ... After round 20, the monkeys are holding items with these worry levels: Monkey 0: 10, 12, 14, 26, 34 Monkey 1: 245, 93, 53, 199, 115 Monkey 2: Monkey 3: Chasing all of the monkeys at once is impossible; you're going to have to focus on the two most active monkeys if you want any hope of getting your stuff back. Count the total number of times each monkey inspects items over 20 rounds: Monkey 0 inspected items 101 times. Monkey 1 inspected items 95 times. Monkey 2 inspected items 7 times. Monkey 3 inspected items 105 times. In this example, the two most active monkeys inspected items 101 and 105 times. The level of monkey business in this situation can be found by multiplying these together: 10605. Figure out which monkeys to chase by counting how many items they inspect over 20 rounds. What is the level of monkey business after 20 rounds of stuff-slinging simian shenanigans?	67
--- Day 17: Two Steps Forward --- You're trying to access a secure vault protected by a 4x4 grid of small rooms connected by doors. You start in the top-left room (marked S), and you can access the vault (marked V) once you reach the bottom-right room: ######### #S\| \| \| # #-#-#-#-# # \| \| \| # #-#-#-#-# # \| \| \| # #-#-#-#-# # \| \| \| ####### V Fixed walls are marked with #, and doors are marked with - or \|. The doors in your current room are either open or closed (and locked) based on the hexadecimal MD5 hash of a passcode (your puzzle input) followed by a sequence of uppercase characters representing the path you have taken so far (U for up, D for down, L for left, and R for right). Only the first four characters of the hash are used; they represent, respectively, the doors up, down, left, and right from your current position. Any b, c, d, e, or f means that the corresponding door is open; any other character (any number or a) means that the corresponding door is closed and locked. To access the vault, all you need to do is reach the bottom-right room; reaching this room opens the vault and all doors in the maze. For example, suppose the passcode is hijkl. Initially, you have taken no steps, and so your path is empty: you simply find the MD5 hash of hijkl alone. The first four characters of this hash are ced9, which indicate that up is open (c), down is open (e), left is open (d), and right is closed and locked (9). Because you start in the top-left corner, there are no "up" or "left" doors to be open, so your only choice is down. Next, having gone only one step (down, or D), you find the hash of hijklD. This produces f2bc, which indicates that you can go back up, left (but that's a wall), or right. Going right means hashing hijklDR to get 5745 - all doors closed and locked. However, going up instead is worthwhile: even though it returns you to the room you started in, your path would then be DU, opening a different set of doors. After going DU (and then hashing hijklDU to get 528e), only the right door is open; after going DUR, all doors lock. (Fortunately, your actual passcode is not hijkl). Passcodes actually used by Easter Bunny Vault Security do allow access to the vault if you know the right path. For example: If your passcode were ihgpwlah, the shortest path would be DDRRRD. With kglvqrro, the shortest path would be DDUDRLRRUDRD. With ulqzkmiv, the shortest would be DRURDRUDDLLDLUURRDULRLDUUDDDRR. Given your vault's passcode, what is the shortest path (the actual path, not just the length) to reach the vault? Your puzzle answer was DUDRLRRDDR. --- Part Two --- You're curious how robust this security solution really is, and so you decide to find longer and longer paths which still provide access to the vault. You remember that paths always end the first time they reach the bottom-right room (that is, they can never pass through it, only end in it). For example: If your passcode were ihgpwlah, the longest path would take 370 steps. With kglvqrro, the longest path would be 492 steps long. With ulqzkmiv, the longest path would be 830 steps long. What is the length of the longest path that reaches the vault?	68
--- Day 7: The Treachery of Whales --- A giant whale has decided your submarine is its next meal, and it's much faster than you are. There's nowhere to run! Suddenly, a swarm of crabs (each in its own tiny submarine - it's too deep for them otherwise) zooms in to rescue you! They seem to be preparing to blast a hole in the ocean floor; sensors indicate a massive underground cave system just beyond where they're aiming! The crab submarines all need to be aligned before they'll have enough power to blast a large enough hole for your submarine to get through. However, it doesn't look like they'll be aligned before the whale catches you! Maybe you can help? There's one major catch - crab submarines can only move horizontally. You quickly make a list of the horizontal position of each crab (your puzzle input). Crab submarines have limited fuel, so you need to find a way to make all of their horizontal positions match while requiring them to spend as little fuel as possible. For example, consider the following horizontal positions: 16,1,2,0,4,2,7,1,2,14 This means there's a crab with horizontal position 16, a crab with horizontal position 1, and so on. Each change of 1 step in horizontal position of a single crab costs 1 fuel. You could choose any horizontal position to align them all on, but the one that costs the least fuel is horizontal position 2: Move from 16 to 2: 14 fuel Move from 1 to 2: 1 fuel Move from 2 to 2: 0 fuel Move from 0 to 2: 2 fuel Move from 4 to 2: 2 fuel Move from 2 to 2: 0 fuel Move from 7 to 2: 5 fuel Move from 1 to 2: 1 fuel Move from 2 to 2: 0 fuel Move from 14 to 2: 12 fuel This costs a total of 37 fuel. This is the cheapest possible outcome; more expensive outcomes include aligning at position 1 (41 fuel), position 3 (39 fuel), or position 10 (71 fuel). Determine the horizontal position that the crabs can align to using the least fuel possible. How much fuel must they spend to align to that position? Your puzzle answer was 351901. --- Part Two --- The crabs don't seem interested in your proposed solution. Perhaps you misunderstand crab engineering? As it turns out, crab submarine engines don't burn fuel at a constant rate. Instead, each change of 1 step in horizontal position costs 1 more unit of fuel than the last: the first step costs 1, the second step costs 2, the third step costs 3, and so on. As each crab moves, moving further becomes more expensive. This changes the best horizontal position to align them all on; in the example above, this becomes 5: Move from 16 to 5: 66 fuel Move from 1 to 5: 10 fuel Move from 2 to 5: 6 fuel Move from 0 to 5: 15 fuel Move from 4 to 5: 1 fuel Move from 2 to 5: 6 fuel Move from 7 to 5: 3 fuel Move from 1 to 5: 10 fuel Move from 2 to 5: 6 fuel Move from 14 to 5: 45 fuel This costs a total of 168 fuel. This is the new cheapest possible outcome; the old alignment position (2) now costs 206 fuel instead. Determine the horizontal position that the crabs can align to using the least fuel possible so they can make you an escape route! How much fuel must they spend to align to that position?	69
--- Day 10: Hoof It --- You all arrive at a Lava Production Facility on a floating island in the sky. As the others begin to search the massive industrial complex, you feel a small nose boop your leg and look down to discover a reindeer wearing a hard hat. The reindeer is holding a book titled "Lava Island Hiking Guide". However, when you open the book, you discover that most of it seems to have been scorched by lava! As you're about to ask how you can help, the reindeer brings you a blank topographic map of the surrounding area (your puzzle input) and looks up at you excitedly. Perhaps you can help fill in the missing hiking trails? The topographic map indicates the height at each position using a scale from 0 (lowest) to 9 (highest). For example: 0123 1234 8765 9876 Based on un-scorched scraps of the book, you determine that a good hiking trail is as long as possible and has an even, gradual, uphill slope. For all practical purposes, this means that a hiking trail is any path that starts at height 0, ends at height 9, and always increases by a height of exactly 1 at each step. Hiking trails never include diagonal steps - only up, down, left, or right (from the perspective of the map). You look up from the map and notice that the reindeer has helpfully begun to construct a small pile of pencils, markers, rulers, compasses, stickers, and other equipment you might need to update the map with hiking trails. A trailhead is any position that starts one or more hiking trails - here, these positions will always have height 0. Assembling more fragments of pages, you establish that a trailhead's score is the number of 9-height positions reachable from that trailhead via a hiking trail. In the above example, the single trailhead in the top left corner has a score of 1 because it can reach a single 9 (the one in the bottom left). This trailhead has a score of 2: ...0... ...1... ...2... 6543456 7.....7 8.....8 9.....9 (The positions marked . are impassable tiles to simplify these examples; they do not appear on your actual topographic map.) This trailhead has a score of 4 because every 9 is reachable via a hiking trail except the one immediately to the left of the trailhead: ..90..9 ...1.98 ...2..7 6543456 765.987 876.... 987.... This topographic map contains two trailheads; the trailhead at the top has a score of 1, while the trailhead at the bottom has a score of 2: 10..9.. 2...8.. 3...7.. 4567654 ...8..3 ...9..2 .....01 Here's a larger example: 89010123 78121874 87430965 96549874 45678903 32019012 01329801 10456732 This larger example has 9 trailheads. Considering the trailheads in reading order, they have scores of 5, 6, 5, 3, 1, 3, 5, 3, and 5. Adding these scores together, the sum of the scores of all trailheads is 36. The reindeer gleefully carries over a protractor and adds it to the pile. What is the sum of the scores of all trailheads on your topographic map? Your puzzle answer was 459. The first half of this puzzle is complete! It provides one gold star: * --- Part Two --- The reindeer spends a few minutes reviewing your hiking trail map before realizing something, disappearing for a few minutes, and finally returning with yet another slightly-charred piece of paper. The paper describes a second way to measure a trailhead called its rating. A trailhead's rating is the number of distinct hiking trails which begin at that trailhead. For example: .....0. ..4321. ..5..2. ..6543. ..7..4. ..8765. ..9.... The above map has a single trailhead; its rating is 3 because there are exactly three distinct hiking trails which begin at that position: .....0. .....0. .....0. ..4321. .....1. .....1. ..5.... .....2. .....2. ..6.... ..6543. .....3. ..7.... ..7.... .....4. ..8.... ..8.... ..8765. ..9.... ..9.... ..9.... Here is a map containing a single trailhead with rating 13: ..90..9 ...1.98 ...2..7 6543456 765.987 876.... 987.... This map contains a single trailhead with rating 227 (because there are 121 distinct hiking trails that lead to the 9 on the right edge and 106 that lead to the 9 on the bottom edge): 012345 123456 234567 345678 4.6789 56789. Here's the larger example from before: 89010123 78121874 87430965 96549874 45678903 32019012 01329801 10456732 Considering its trailheads in reading order, they have ratings of 20, 24, 10, 4, 1, 4, 5, 8, and 5. The sum of all trailhead ratings in this larger example topographic map is 81. You're not sure how, but the reindeer seems to have crafted some tiny flags out of toothpicks and bits of paper and is using them to mark trailheads on your topographic map. What is the sum of the ratings of all trailheads?	70
--- Day 3: Perfectly Spherical Houses in a Vacuum --- Santa is delivering presents to an infinite two-dimensional grid of houses. He begins by delivering a present to the house at his starting location, and then an elf at the North Pole calls him via radio and tells him where to move next. Moves are always exactly one house to the north (^), south (v), east (>), or west (<). After each move, he delivers another present to the house at his new location. However, the elf back at the north pole has had a little too much eggnog, and so his directions are a little off, and Santa ends up visiting some houses more than once. How many houses receive at least one present? For example: > delivers presents to 2 houses: one at the starting location, and one to the east. ^>v< delivers presents to 4 houses in a square, including twice to the house at his starting/ending location. ^v^v^v^v^v delivers a bunch of presents to some very lucky children at only 2 houses. Your puzzle answer was 2565. --- Part Two --- The next year, to speed up the process, Santa creates a robot version of himself, Robo-Santa, to deliver presents with him. Santa and Robo-Santa start at the same location (delivering two presents to the same starting house), then take turns moving based on instructions from the elf, who is eggnoggedly reading from the same script as the previous year. This year, how many houses receive at least one present? For example: ^v delivers presents to 3 houses, because Santa goes north, and then Robo-Santa goes south. ^>v< now delivers presents to 3 houses, and Santa and Robo-Santa end up back where they started. ^v^v^v^v^v now delivers presents to 11 houses, with Santa going one direction and Robo-Santa going the other.	71
--- Day 2: 1202 Program Alarm --- On the way to your gravity assist around the Moon, your ship computer beeps angrily about a "1202 program alarm". On the radio, an Elf is already explaining how to handle the situation: "Don't worry, that's perfectly norma--" The ship computer bursts into flames. You notify the Elves that the computer's magic smoke seems to have escaped. "That computer ran Intcode programs like the gravity assist program it was working on; surely there are enough spare parts up there to build a new Intcode computer!" An Intcode program is a list of integers separated by commas (like 1,0,0,3,99). To run one, start by looking at the first integer (called position 0). Here, you will find an opcode - either 1, 2, or 99. The opcode indicates what to do; for example, 99 means that the program is finished and should immediately halt. Encountering an unknown opcode means something went wrong. Opcode 1 adds together numbers read from two positions and stores the result in a third position. The three integers immediately after the opcode tell you these three positions - the first two indicate the positions from which you should read the input values, and the third indicates the position at which the output should be stored. For example, if your Intcode computer encounters 1,10,20,30, it should read the values at positions 10 and 20, add those values, and then overwrite the value at position 30 with their sum. Opcode 2 works exactly like opcode 1, except it multiplies the two inputs instead of adding them. Again, the three integers after the opcode indicate where the inputs and outputs are, not their values. Once you're done processing an opcode, move to the next one by stepping forward 4 positions. For example, suppose you have the following program: 1,9,10,3,2,3,11,0,99,30,40,50 For the purposes of illustration, here is the same program split into multiple lines: 1,9,10,3, 2,3,11,0, 99, 30,40,50 The first four integers, 1,9,10,3, are at positions 0, 1, 2, and 3. Together, they represent the first opcode (1, addition), the positions of the two inputs (9 and 10), and the position of the output (3). To handle this opcode, you first need to get the values at the input positions: position 9 contains 30, and position 10 contains 40. Add these numbers together to get 70. Then, store this value at the output position; here, the output position (3) is at position 3, so it overwrites itself. Afterward, the program looks like this: 1,9,10,70, 2,3,11,0, 99, 30,40,50 Step forward 4 positions to reach the next opcode, 2. This opcode works just like the previous, but it multiplies instead of adding. The inputs are at positions 3 and 11; these positions contain 70 and 50 respectively. Multiplying these produces 3500; this is stored at position 0: 3500,9,10,70, 2,3,11,0, 99, 30,40,50 Stepping forward 4 more positions arrives at opcode 99, halting the program. Here are the initial and final states of a few more small programs: 1,0,0,0,99 becomes 2,0,0,0,99 (1 + 1 = 2). 2,3,0,3,99 becomes 2,3,0,6,99 (3 * 2 = 6). 2,4,4,5,99,0 becomes 2,4,4,5,99,9801 (99 * 99 = 9801). 1,1,1,4,99,5,6,0,99 becomes 30,1,1,4,2,5,6,0,99. Once you have a working computer, the first step is to restore the gravity assist program (your puzzle input) to the "1202 program alarm" state it had just before the last computer caught fire. To do this, before running the program, replace position 1 with the value 12 and replace position 2 with the value 2. What value is left at position 0 after the program halts?	72
--- Day 12: JSAbacusFramework.io --- Santa's Accounting-Elves need help balancing the books after a recent order. Unfortunately, their accounting software uses a peculiar storage format. That's where you come in. They have a JSON document which contains a variety of things: arrays ([1,2,3]), objects ({"a":1, "b":2}), numbers, and strings. Your first job is to simply find all of the numbers throughout the document and add them together. For example: [1,2,3] and {"a":2,"b":4} both have a sum of 6. [[[3]]] and {"a":{"b":4},"c":-1} both have a sum of 3. {"a":[-1,1]} and [-1,{"a":1}] both have a sum of 0. [] and {} both have a sum of 0. You will not encounter any strings containing numbers. What is the sum of all numbers in the document?	73
--- Day 25: The Halting Problem --- Following the twisty passageways deeper and deeper into the CPU, you finally reach the core of the computer. Here, in the expansive central chamber, you find a grand apparatus that fills the entire room, suspended nanometers above your head. You had always imagined CPUs to be noisy, chaotic places, bustling with activity. Instead, the room is quiet, motionless, and dark. Suddenly, you and the CPU's garbage collector startle each other. "It's not often we get many visitors here!", he says. You inquire about the stopped machinery. "It stopped milliseconds ago; not sure why. I'm a garbage collector, not a doctor." You ask what the machine is for. "Programs these days, don't know their origins. That's the Turing machine! It's what makes the whole computer work." You try to explain that Turing machines are merely models of computation, but he cuts you off. "No, see, that's just what they want you to think. Ultimately, inside every CPU, there's a Turing machine driving the whole thing! Too bad this one's broken. We're doomed!" You ask how you can help. "Well, unfortunately, the only way to get the computer running again would be to create a whole new Turing machine from scratch, but there's no way you can-" He notices the look on your face, gives you a curious glance, shrugs, and goes back to sweeping the floor. You find the Turing machine blueprints (your puzzle input) on a tablet in a nearby pile of debris. Looking back up at the broken Turing machine above, you can start to identify its parts: A tape which contains 0 repeated infinitely to the left and right. A cursor, which can move left or right along the tape and read or write values at its current position. A set of states, each containing rules about what to do based on the current value under the cursor. Each slot on the tape has two possible values: 0 (the starting value for all slots) and 1. Based on whether the cursor is pointing at a 0 or a 1, the current state says what value to write at the current position of the cursor, whether to move the cursor left or right one slot, and which state to use next. For example, suppose you found the following blueprint: Begin in state A. Perform a diagnostic checksum after 6 steps. In state A: If the current value is 0: - Write the value 1. - Move one slot to the right. - Continue with state B. If the current value is 1: - Write the value 0. - Move one slot to the left. - Continue with state B. In state B: If the current value is 0: - Write the value 1. - Move one slot to the left. - Continue with state A. If the current value is 1: - Write the value 1. - Move one slot to the right. - Continue with state A. Running it until the number of steps required to take the listed diagnostic checksum would result in the following tape configurations (with the cursor marked in square brackets): ... 0 0 0 [0] 0 0 ... (before any steps; about to run state A) ... 0 0 0 1 [0] 0 ... (after 1 step; about to run state B) ... 0 0 0 [1] 1 0 ... (after 2 steps; about to run state A) ... 0 0 [0] 0 1 0 ... (after 3 steps; about to run state B) ... 0 [0] 1 0 1 0 ... (after 4 steps; about to run state A) ... 0 1 [1] 0 1 0 ... (after 5 steps; about to run state B) ... 0 1 1 [0] 1 0 ... (after 6 steps; about to run state A) The CPU can confirm that the Turing machine is working by taking a diagnostic checksum after a specific number of steps (given in the blueprint). Once the specified number of steps have been executed, the Turing machine should pause; once it does, count the number of times 1 appears on the tape. In the above example, the diagnostic checksum is 3. Recreate the Turing machine and save the computer! What is the diagnostic checksum it produces once it's working again?	74
--- Day 14: Chocolate Charts --- You finally have a chance to look at all of the produce moving around. Chocolate, cinnamon, mint, chili peppers, nutmeg, vanilla... the Elves must be growing these plants to make hot chocolate! As you realize this, you hear a conversation in the distance. When you go to investigate, you discover two Elves in what appears to be a makeshift underground kitchen/laboratory. The Elves are trying to come up with the ultimate hot chocolate recipe; they're even maintaining a scoreboard which tracks the quality score (0-9) of each recipe. Only two recipes are on the board: the first recipe got a score of 3, the second, 7. Each of the two Elves has a current recipe: the first Elf starts with the first recipe, and the second Elf starts with the second recipe. To create new recipes, the two Elves combine their current recipes. This creates new recipes from the digits of the sum of the current recipes' scores. With the current recipes' scores of 3 and 7, their sum is 10, and so two new recipes would be created: the first with score 1 and the second with score 0. If the current recipes' scores were 2 and 3, the sum, 5, would only create one recipe (with a score of 5) with its single digit. The new recipes are added to the end of the scoreboard in the order they are created. So, after the first round, the scoreboard is 3, 7, 1, 0. After all new recipes are added to the scoreboard, each Elf picks a new current recipe. To do this, the Elf steps forward through the scoreboard a number of recipes equal to 1 plus the score of their current recipe. So, after the first round, the first Elf moves forward 1 + 3 = 4 times, while the second Elf moves forward 1 + 7 = 8 times. If they run out of recipes, they loop back around to the beginning. After the first round, both Elves happen to loop around until they land on the same recipe that they had in the beginning; in general, they will move to different recipes. Drawing the first Elf as parentheses and the second Elf as square brackets, they continue this process: (3)[7] (3)[7] 1 0 3 7 1 [0](1) 0 3 7 1 0 [1] 0 (1) (3) 7 1 0 1 0 [1] 2 3 7 1 0 (1) 0 1 2 [4] 3 7 1 [0] 1 0 (1) 2 4 5 3 7 1 0 [1] 0 1 2 (4) 5 1 3 (7) 1 0 1 0 [1] 2 4 5 1 5 3 7 1 0 1 0 1 2 [4](5) 1 5 8 3 (7) 1 0 1 0 1 2 4 5 1 5 8 [9] 3 7 1 0 1 0 1 [2] 4 (5) 1 5 8 9 1 6 3 7 1 0 1 0 1 2 4 5 [1] 5 8 9 1 (6) 7 3 7 1 0 (1) 0 1 2 4 5 1 5 [8] 9 1 6 7 7 3 7 [1] 0 1 0 (1) 2 4 5 1 5 8 9 1 6 7 7 9 3 7 1 0 [1] 0 1 2 (4) 5 1 5 8 9 1 6 7 7 9 2 The Elves think their skill will improve after making a few recipes (your puzzle input). However, that could take ages; you can speed this up considerably by identifying the scores of the ten recipes after that. For example: If the Elves think their skill will improve after making 9 recipes, the scores of the ten recipes after the first nine on the scoreboard would be 5158916779 (highlighted in the last line of the diagram). After 5 recipes, the scores of the next ten would be 0124515891. After 18 recipes, the scores of the next ten would be 9251071085. After 2018 recipes, the scores of the next ten would be 5941429882. What are the scores of the ten recipes immediately after the number of recipes in your puzzle input?	75
--- Day 19: Monster Messages --- You land in an airport surrounded by dense forest. As you walk to your high-speed train, the Elves at the Mythical Information Bureau contact you again. They think their satellite has collected an image of a sea monster! Unfortunately, the connection to the satellite is having problems, and many of the messages sent back from the satellite have been corrupted. They sent you a list of the rules valid messages should obey and a list of received messages they've collected so far (your puzzle input). The rules for valid messages (the top part of your puzzle input) are numbered and build upon each other. For example: 0: 1 2 1: "a" 2: 1 3 \| 3 1 3: "b" Some rules, like 3: "b", simply match a single character (in this case, b). The remaining rules list the sub-rules that must be followed; for example, the rule 0: 1 2 means that to match rule 0, the text being checked must match rule 1, and the text after the part that matched rule 1 must then match rule 2. Some of the rules have multiple lists of sub-rules separated by a pipe (\|). This means that at least one list of sub-rules must match. (The ones that match might be different each time the rule is encountered.) For example, the rule 2: 1 3 \| 3 1 means that to match rule 2, the text being checked must match rule 1 followed by rule 3 or it must match rule 3 followed by rule 1. Fortunately, there are no loops in the rules, so the list of possible matches will be finite. Since rule 1 matches a and rule 3 matches b, rule 2 matches either ab or ba. Therefore, rule 0 matches aab or aba. Here's a more interesting example: 0: 4 1 5 1: 2 3 \| 3 2 2: 4 4 \| 5 5 3: 4 5 \| 5 4 4: "a" 5: "b" Here, because rule 4 matches a and rule 5 matches b, rule 2 matches two letters that are the same (aa or bb), and rule 3 matches two letters that are different (ab or ba). Since rule 1 matches rules 2 and 3 once each in either order, it must match two pairs of letters, one pair with matching letters and one pair with different letters. This leaves eight possibilities: aaab, aaba, bbab, bbba, abaa, abbb, baaa, or babb. Rule 0, therefore, matches a (rule 4), then any of the eight options from rule 1, then b (rule 5): aaaabb, aaabab, abbabb, abbbab, aabaab, aabbbb, abaaab, or ababbb. The received messages (the bottom part of your puzzle input) need to be checked against the rules so you can determine which are valid and which are corrupted. Including the rules and the messages together, this might look like: 0: 4 1 5 1: 2 3 \| 3 2 2: 4 4 \| 5 5 3: 4 5 \| 5 4 4: "a" 5: "b" ababbb bababa abbbab aaabbb aaaabbb Your goal is to determine the number of messages that completely match rule 0. In the above example, ababbb and abbbab match, but bababa, aaabbb, and aaaabbb do not, producing the answer 2. The whole message must match all of rule 0; there can't be extra unmatched characters in the message. (For example, aaaabbb might appear to match rule 0 above, but it has an extra unmatched b on the end.) How many messages completely match rule 0?	76
--- Day 15: Timing is Everything --- The halls open into an interior plaza containing a large kinetic sculpture. The sculpture is in a sealed enclosure and seems to involve a set of identical spherical capsules that are carried to the top and allowed to bounce through the maze of spinning pieces. Part of the sculpture is even interactive! When a button is pressed, a capsule is dropped and tries to fall through slots in a set of rotating discs to finally go through a little hole at the bottom and come out of the sculpture. If any of the slots aren't aligned with the capsule as it passes, the capsule bounces off the disc and soars away. You feel compelled to get one of those capsules. The discs pause their motion each second and come in different sizes; they seem to each have a fixed number of positions at which they stop. You decide to call the position with the slot 0, and count up for each position it reaches next. Furthermore, the discs are spaced out so that after you push the button, one second elapses before the first disc is reached, and one second elapses as the capsule passes from one disc to the one below it. So, if you push the button at time=100, then the capsule reaches the top disc at time=101, the second disc at time=102, the third disc at time=103, and so on. The button will only drop a capsule at an integer time - no fractional seconds allowed. For example, at time=0, suppose you see the following arrangement: Disc #1 has 5 positions; at time=0, it is at position 4. Disc #2 has 2 positions; at time=0, it is at position 1. If you press the button exactly at time=0, the capsule would start to fall; it would reach the first disc at time=1. Since the first disc was at position 4 at time=0, by time=1 it has ticked one position forward. As a five-position disc, the next position is 0, and the capsule falls through the slot. Then, at time=2, the capsule reaches the second disc. The second disc has ticked forward two positions at this point: it started at position 1, then continued to position 0, and finally ended up at position 1 again. Because there's only a slot at position 0, the capsule bounces away. If, however, you wait until time=5 to push the button, then when the capsule reaches each disc, the first disc will have ticked forward 5+1 = 6 times (to position 0), and the second disc will have ticked forward 5+2 = 7 times (also to position 0). In this case, the capsule would fall through the discs and come out of the machine. However, your situation has more than two discs; you've noted their positions in your puzzle input. What is the first time you can press the button to get a capsule?	77
--- Day 15: Chiton --- You've almost reached the exit of the cave, but the walls are getting closer together. Your submarine can barely still fit, though; the main problem is that the walls of the cave are covered in chitons, and it would be best not to bump any of them. The cavern is large, but has a very low ceiling, restricting your motion to two dimensions. The shape of the cavern resembles a square; a quick scan of chiton density produces a map of risk level throughout the cave (your puzzle input). For example: 1163751742 1381373672 2136511328 3694931569 7463417111 1319128137 1359912421 3125421639 1293138521 2311944581 You start in the top left position, your destination is the bottom right position, and you cannot move diagonally. The number at each position is its risk level; to determine the total risk of an entire path, add up the risk levels of each position you enter (that is, don't count the risk level of your starting position unless you enter it; leaving it adds no risk to your total). Your goal is to find a path with the lowest total risk. In this example, a path with the lowest total risk is highlighted here: 1163751742 1381373672 2136511328 3694931569 7463417111 1319128137 1359912421 3125421639 1293138521 2311944581 The total risk of this path is 40 (the starting position is never entered, so its risk is not counted). What is the lowest total risk of any path from the top left to the bottom right? Your puzzle answer was 398. --- Part Two --- Now that you know how to find low-risk paths in the cave, you can try to find your way out. The entire cave is actually five times larger in both dimensions than you thought; the area you originally scanned is just one tile in a 5x5 tile area that forms the full map. Your original map tile repeats to the right and downward; each time the tile repeats to the right or downward, all of its risk levels are 1 higher than the tile immediately up or left of it. However, risk levels above 9 wrap back around to 1. So, if your original map had some position with a risk level of 8, then that same position on each of the 25 total tiles would be as follows: 8 9 1 2 3 9 1 2 3 4 1 2 3 4 5 2 3 4 5 6 3 4 5 6 7 Each single digit above corresponds to the example position with a value of 8 on the top-left tile. Because the full map is actually five times larger in both dimensions, that position appears a total of 25 times, once in each duplicated tile, with the values shown above. Here is the full five-times-as-large version of the first example above, with the original map in the top left corner highlighted: 11637517422274862853338597396444961841755517295286 13813736722492484783351359589446246169155735727126 21365113283247622439435873354154698446526571955763 36949315694715142671582625378269373648937148475914 74634171118574528222968563933317967414442817852555 13191281372421239248353234135946434524615754563572 13599124212461123532357223464346833457545794456865 31254216394236532741534764385264587549637569865174 12931385212314249632342535174345364628545647573965 23119445813422155692453326671356443778246755488935 22748628533385973964449618417555172952866628316397 24924847833513595894462461691557357271266846838237 32476224394358733541546984465265719557637682166874 47151426715826253782693736489371484759148259586125 85745282229685639333179674144428178525553928963666 24212392483532341359464345246157545635726865674683 24611235323572234643468334575457944568656815567976 42365327415347643852645875496375698651748671976285 23142496323425351743453646285456475739656758684176 34221556924533266713564437782467554889357866599146 33859739644496184175551729528666283163977739427418 35135958944624616915573572712668468382377957949348 43587335415469844652657195576376821668748793277985 58262537826937364893714847591482595861259361697236 96856393331796741444281785255539289636664139174777 35323413594643452461575456357268656746837976785794 35722346434683345754579445686568155679767926678187 53476438526458754963756986517486719762859782187396 34253517434536462854564757396567586841767869795287 45332667135644377824675548893578665991468977611257 44961841755517295286662831639777394274188841538529 46246169155735727126684683823779579493488168151459 54698446526571955763768216687487932779859814388196 69373648937148475914825958612593616972361472718347 17967414442817852555392896366641391747775241285888 46434524615754563572686567468379767857948187896815 46833457545794456865681556797679266781878137789298 64587549637569865174867197628597821873961893298417 45364628545647573965675868417678697952878971816398 56443778246755488935786659914689776112579188722368 55172952866628316397773942741888415385299952649631 57357271266846838237795794934881681514599279262561 65719557637682166874879327798598143881961925499217 71484759148259586125936169723614727183472583829458 28178525553928963666413917477752412858886352396999 57545635726865674683797678579481878968159298917926 57944568656815567976792667818781377892989248891319 75698651748671976285978218739618932984172914319528 56475739656758684176786979528789718163989182927419 67554889357866599146897761125791887223681299833479 Equipped with the full map, you can now find a path from the top left corner to the bottom right corner with the lowest total risk: 11637517422274862853338597396444961841755517295286 13813736722492484783351359589446246169155735727126 21365113283247622439435873354154698446526571955763 36949315694715142671582625378269373648937148475914 74634171118574528222968563933317967414442817852555 13191281372421239248353234135946434524615754563572 13599124212461123532357223464346833457545794456865 31254216394236532741534764385264587549637569865174 12931385212314249632342535174345364628545647573965 23119445813422155692453326671356443778246755488935 22748628533385973964449618417555172952866628316397 24924847833513595894462461691557357271266846838237 32476224394358733541546984465265719557637682166874 47151426715826253782693736489371484759148259586125 85745282229685639333179674144428178525553928963666 24212392483532341359464345246157545635726865674683 24611235323572234643468334575457944568656815567976 42365327415347643852645875496375698651748671976285 23142496323425351743453646285456475739656758684176 34221556924533266713564437782467554889357866599146 33859739644496184175551729528666283163977739427418 35135958944624616915573572712668468382377957949348 43587335415469844652657195576376821668748793277985 58262537826937364893714847591482595861259361697236 96856393331796741444281785255539289636664139174777 35323413594643452461575456357268656746837976785794 35722346434683345754579445686568155679767926678187 53476438526458754963756986517486719762859782187396 34253517434536462854564757396567586841767869795287 45332667135644377824675548893578665991468977611257 44961841755517295286662831639777394274188841538529 46246169155735727126684683823779579493488168151459 54698446526571955763768216687487932779859814388196 69373648937148475914825958612593616972361472718347 17967414442817852555392896366641391747775241285888 46434524615754563572686567468379767857948187896815 46833457545794456865681556797679266781878137789298 64587549637569865174867197628597821873961893298417 45364628545647573965675868417678697952878971816398 56443778246755488935786659914689776112579188722368 55172952866628316397773942741888415385299952649631 57357271266846838237795794934881681514599279262561 65719557637682166874879327798598143881961925499217 71484759148259586125936169723614727183472583829458 28178525553928963666413917477752412858886352396999 57545635726865674683797678579481878968159298917926 57944568656815567976792667818781377892989248891319 75698651748671976285978218739618932984172914319528 56475739656758684176786979528789718163989182927419 67554889357866599146897761125791887223681299833479 The total risk of this path is 315 (the starting position is still never entered, so its risk is not counted). Using the full map, what is the lowest total risk of any path from the top left to the bottom right?	78
--- Day 9: Mirage Maintenance --- You ride the camel through the sandstorm and stop where the ghost's maps told you to stop. The sandstorm subsequently subsides, somehow seeing you standing at an oasis! The camel goes to get some water and you stretch your neck. As you look up, you discover what must be yet another giant floating island, this one made of metal! That must be where the parts to fix the sand machines come from. There's even a hang glider partially buried in the sand here; once the sun rises and heats up the sand, you might be able to use the glider and the hot air to get all the way up to the metal island! While you wait for the sun to rise, you admire the oasis hidden here in the middle of Desert Island. It must have a delicate ecosystem; you might as well take some ecological readings while you wait. Maybe you can report any environmental instabilities you find to someone so the oasis can be around for the next sandstorm-worn traveler. You pull out your handy Oasis And Sand Instability Sensor and analyze your surroundings. The OASIS produces a report of many values and how they are changing over time (your puzzle input). Each line in the report contains the history of a single value. For example: 0 3 6 9 12 15 1 3 6 10 15 21 10 13 16 21 30 45 To best protect the oasis, your environmental report should include a prediction of the next value in each history. To do this, start by making a new sequence from the difference at each step of your history. If that sequence is not all zeroes, repeat this process, using the sequence you just generated as the input sequence. Once all of the values in your latest sequence are zeroes, you can extrapolate what the next value of the original history should be. In the above dataset, the first history is 0 3 6 9 12 15. Because the values increase by 3 each step, the first sequence of differences that you generate will be 3 3 3 3 3. Note that this sequence has one fewer value than the input sequence because at each step it considers two numbers from the input. Since these values aren't all zero, repeat the process: the values differ by 0 at each step, so the next sequence is 0 0 0 0. This means you have enough information to extrapolate the history! Visually, these sequences can be arranged like this: 0 3 6 9 12 15 3 3 3 3 3 0 0 0 0 To extrapolate, start by adding a new zero to the end of your list of zeroes; because the zeroes represent differences between the two values above them, this also means there is now a placeholder in every sequence above it: 0 3 6 9 12 15 B 3 3 3 3 3 A 0 0 0 0 0 You can then start filling in placeholders from the bottom up. A needs to be the result of increasing 3 (the value to its left) by 0 (the value below it); this means A must be 3: 0 3 6 9 12 15 B 3 3 3 3 3 3 0 0 0 0 0 Finally, you can fill in B, which needs to be the result of increasing 15 (the value to its left) by 3 (the value below it), or 18: 0 3 6 9 12 15 18 3 3 3 3 3 3 0 0 0 0 0 So, the next value of the first history is 18. Finding all-zero differences for the second history requires an additional sequence: 1 3 6 10 15 21 2 3 4 5 6 1 1 1 1 0 0 0 Then, following the same process as before, work out the next value in each sequence from the bottom up: 1 3 6 10 15 21 28 2 3 4 5 6 7 1 1 1 1 1 0 0 0 0 So, the next value of the second history is 28. The third history requires even more sequences, but its next value can be found the same way: 10 13 16 21 30 45 68 3 3 5 9 15 23 0 2 4 6 8 2 2 2 2 0 0 0 So, the next value of the third history is 68. If you find the next value for each history in this example and add them together, you get 114. Analyze your OASIS report and extrapolate the next value for each history. What is the sum of these extrapolated values?	79
--- Day 20: Jurassic Jigsaw --- The high-speed train leaves the forest and quickly carries you south. You can even see a desert in the distance! Since you have some spare time, you might as well see if there was anything interesting in the image the Mythical Information Bureau satellite captured. After decoding the satellite messages, you discover that the data actually contains many small images created by the satellite's camera array. The camera array consists of many cameras; rather than produce a single square image, they produce many smaller square image tiles that need to be reassembled back into a single image. Each camera in the camera array returns a single monochrome image tile with a random unique ID number. The tiles (your puzzle input) arrived in a random order. Worse yet, the camera array appears to be malfunctioning: each image tile has been rotated and flipped to a random orientation. Your first task is to reassemble the original image by orienting the tiles so they fit together. To show how the tiles should be reassembled, each tile's image data includes a border that should line up exactly with its adjacent tiles. All tiles have this border, and the border lines up exactly when the tiles are both oriented correctly. Tiles at the edge of the image also have this border, but the outermost edges won't line up with any other tiles. For example, suppose you have the following nine tiles: Tile 2311: ..##.#..#. ##..#..... #...##..#. ####.#...# ##.##.###. ##...#.### .#.#.#..## ..#....#.. ###...#.#. ..###..### Tile 1951: #.##...##. #.####...# .....#..## #...###### .##.#....# .###.##### ###.##.##. .###....#. ..#.#..#.# #...##.#.. Tile 1171: ####...##. #..##.#..# ##.#..#.#. .###.####. ..###.#### .##....##. .#...####. #.##.####. ####..#... .....##... Tile 1427: ###.##.#.. .#..#.##.. .#.##.#..# #.#.#.##.# ....#...## ...##..##. ...#.##### .#.####.#. ..#..###.# ..##.#..#. Tile 1489: ##.#.#.... ..##...#.. .##..##... ..#...#... #####...#. #..#.#.#.# ...#.#.#.. ##.#...##. ..##.##.## ###.##.#.. Tile 2473: #....####. #..#.##... #.##..#... ######.#.# .#...#.#.# .######### .###.#..#. ########.# ##...##.#. ..###.#.#. Tile 2971: ..#.#....# #...###... #.#.###... ##.##..#.. .#####..## .#..####.# #..#.#..#. ..####.### ..#.#.###. ...#.#.#.# Tile 2729: ...#.#.#.# ####.#.... ..#.#..... ....#..#.# .##..##.#. .#.####... ####.#.#.. ##.####... ##..#.##.. #.##...##. Tile 3079: #.#.#####. .#..###### ..#....... ######.... ####.#..#. .#...#.##. #.#####.## ..#.###... ..#....... ..#.###... By rotating, flipping, and rearranging them, you can find a square arrangement that causes all adjacent borders to line up: #...##.#.. ..###..### #.#.#####. ..#.#..#.# ###...#.#. .#..###### .###....#. ..#....#.. ..#....... ###.##.##. .#.#.#..## ######.... .###.##### ##...#.### ####.#..#. .##.#....# ##.##.###. .#...#.##. #...###### ####.#...# #.#####.## .....#..## #...##..#. ..#.###... #.####...# ##..#..... ..#....... #.##...##. ..##.#..#. ..#.###... #.##...##. ..##.#..#. ..#.###... ##..#.##.. ..#..###.# ##.##....# ##.####... .#.####.#. ..#.###..# ####.#.#.. ...#.##### ###.#..### .#.####... ...##..##. .######.## .##..##.#. ....#...## #.#.#.#... ....#..#.# #.#.#.##.# #.###.###. ..#.#..... .#.##.#..# #.###.##.. ####.#.... .#..#.##.. .######... ...#.#.#.# ###.##.#.. .##...#### ...#.#.#.# ###.##.#.. .##...#### ..#.#.###. ..##.##.## #..#.##..# ..####.### ##.#...##. .#.#..#.## #..#.#..#. ...#.#.#.. .####.###. .#..####.# #..#.#.#.# ####.###.. .#####..## #####...#. .##....##. ##.##..#.. ..#...#... .####...#. #.#.###... .##..##... .####.##.# #...###... ..##...#.. ...#..#### ..#.#....# ##.#.#.... ...##..... For reference, the IDs of the above tiles are: 1951 2311 3079 2729 1427 2473 2971 1489 1171 To check that you've assembled the image correctly, multiply the IDs of the four corner tiles together. If you do this with the assembled tiles from the example above, you get 1951 * 3079 * 2971 * 1171 = 20899048083289. Assemble the tiles into an image. What do you get if you multiply together the IDs of the four corner tiles? Your puzzle answer was 23386616781851. --- Part Two --- Now, you're ready to check the image for sea monsters. The borders of each tile are not part of the actual image; start by removing them. In the example above, the tiles become: .#.#..#. ##...#.# #..##### ###....# .#....#. .#...... ##.##.## #.#.#..# #####... ###.#### #...#.## ###.#..# ##.#.... #.##.### #...#.## ...##### ###.#... .#####.# ....#..# ...##..# .#.###.. .####... #..#.... .#...... #..#.##. .#..###. #.##.... #.####.. #.####.# .#.###.. ###.#.#. ..#.#### ##.#..## #.####.. ..##..## ######.# ##..##.# ...#...# .#.#.#.. ...#..#. .#.#.##. .###.### .#.#.... #.##.#.. .###.##. ###.#... #..#.##. ######.. .#.#.### .##.##.# ..#.##.. .####.## #.#...## #.#..#.# ..#.#..# ..#.#.#. ####.### #..####. ..#.#.#. ###.###. #####..# ####...# ##....## #.##..#. .#...#.. ####...# .#.###.. ##..##.. ####.##. ...###.. .##...#. ..#..### Remove the gaps to form the actual image: .#.#..#.##...#.##..##### ###....#.#....#..#...... ##.##.###.#.#..######... ###.#####...#.#####.#..# ##.#....#.##.####...#.## ...########.#....#####.# ....#..#...##..#.#.###.. .####...#..#.....#...... #..#.##..#..###.#.##.... #.####..#.####.#.#.###.. ###.#.#...#.######.#..## #.####....##..########.# ##..##.#...#...#.#.#.#.. ...#..#..#.#.##..###.### .#.#....#.##.#...###.##. ###.#...#..#.##.######.. .#.#.###.##.##.#..#.##.. .####.###.#...###.#..#.# ..#.#..#..#.#.#.####.### #..####...#.#.#.###.###. #####..#####...###....## #.##..#..#...#..####...# .#.###..##..##..####.##. ...###...##...#...#..### Now, you're ready to search for sea monsters! Because your image is monochrome, a sea monster will look like this: # # ## ## ### # # # # # # When looking for this pattern in the image, the spaces can be anything; only the # need to match. Also, you might need to rotate or flip your image before it's oriented correctly to find sea monsters. In the above image, after flipping and rotating it to the appropriate orientation, there are two sea monsters (marked with O): .####...#####..#...###.. #####..#..#.#.####..#.#. .#.#...#.###...#.##.O#.. #.O.##.OO#.#.OO.##.OOO## ..#O.#O#.O##O..O.#O##.## ...#.#..##.##...#..#..## #.##.#..#.#..#..##.#.#.. .###.##.....#...###.#... #.####.#.#....##.#..#.#. ##...#..#....#..#...#### ..#.##...###..#.#####..# ....#.##.#.#####....#... ..##.##.###.....#.##..#. #...#...###..####....##. .#.##...#.##.#.#.###...# #.###.#..####...##..#... #.###...#.##...#.##O###. .O##.#OO.###OO##..OOO##. ..O#.O..O..O.#O##O##.### #.#..##.########..#..##. #.#####..#.#...##..#.... #....##..#.#########..## #...#.....#..##...###.## #..###....##.#...##.##.# Determine how rough the waters are in the sea monsters' habitat by counting the number of # that are not part of a sea monster. In the above example, the habitat's water roughness is 273. How many # are not part of a sea monster?	80
--- Day 3: Crossed Wires --- The gravity assist was successful, and you're well on your way to the Venus refuelling station. During the rush back on Earth, the fuel management system wasn't completely installed, so that's next on the priority list. Opening the front panel reveals a jumble of wires. Specifically, two wires are connected to a central port and extend outward on a grid. You trace the path each wire takes as it leaves the central port, one wire per line of text (your puzzle input). The wires twist and turn, but the two wires occasionally cross paths. To fix the circuit, you need to find the intersection point closest to the central port. Because the wires are on a grid, use the Manhattan distance for this measurement. While the wires do technically cross right at the central port where they both start, this point does not count, nor does a wire count as crossing with itself. For example, if the first wire's path is R8,U5,L5,D3, then starting from the central port (o), it goes right 8, up 5, left 5, and finally down 3: ........... ........... ........... ....+----+. ....\|....\|. ....\|....\|. ....\|....\|. .........\|. .o-------+. ........... Then, if the second wire's path is U7,R6,D4,L4, it goes up 7, right 6, down 4, and left 4: ........... .+-----+... .\|.....\|... .\|..+--X-+. .\|..\|..\|.\|. .\|.-X--+.\|. .\|..\|....\|. .\|.......\|. .o-------+. ........... These wires cross at two locations (marked X), but the lower-left one is closer to the central port: its distance is 3 + 3 = 6. Here are a few more examples: R75,D30,R83,U83,L12,D49,R71,U7,L72 U62,R66,U55,R34,D71,R55,D58,R83 = distance 159 R98,U47,R26,D63,R33,U87,L62,D20,R33,U53,R51 U98,R91,D20,R16,D67,R40,U7,R15,U6,R7 = distance 135 What is the Manhattan distance from the central port to the closest intersection?	81
--- Day 9: Marble Mania --- You talk to the Elves while you wait for your navigation system to initialize. To pass the time, they introduce you to their favorite marble game. The Elves play this game by taking turns arranging the marbles in a circle according to very particular rules. The marbles are numbered starting with 0 and increasing by 1 until every marble has a number. First, the marble numbered 0 is placed in the circle. At this point, while it contains only a single marble, it is still a circle: the marble is both clockwise from itself and counter-clockwise from itself. This marble is designated the current marble. Then, each Elf takes a turn placing the lowest-numbered remaining marble into the circle between the marbles that are 1 and 2 marbles clockwise of the current marble. (When the circle is large enough, this means that there is one marble between the marble that was just placed and the current marble.) The marble that was just placed then becomes the current marble. However, if the marble that is about to be placed has a number which is a multiple of 23, something entirely different happens. First, the current player keeps the marble they would have placed, adding it to their score. In addition, the marble 7 marbles counter-clockwise from the current marble is removed from the circle and also added to the current player's score. The marble located immediately clockwise of the marble that was removed becomes the new current marble. For example, suppose there are 9 players. After the marble with value 0 is placed in the middle, each player (shown in square brackets) takes a turn. The result of each of those turns would produce circles of marbles like this, where clockwise is to the right and the resulting current marble is in parentheses: [-] (0) [1] 0 (1) [2] 0 (2) 1 [3] 0 2 1 (3) [4] 0 (4) 2 1 3 [5] 0 4 2 (5) 1 3 [6] 0 4 2 5 1 (6) 3 [7] 0 4 2 5 1 6 3 (7) [8] 0 (8) 4 2 5 1 6 3 7 [9] 0 8 4 (9) 2 5 1 6 3 7 [1] 0 8 4 9 2(10) 5 1 6 3 7 [2] 0 8 4 9 2 10 5(11) 1 6 3 7 [3] 0 8 4 9 2 10 5 11 1(12) 6 3 7 [4] 0 8 4 9 2 10 5 11 1 12 6(13) 3 7 [5] 0 8 4 9 2 10 5 11 1 12 6 13 3(14) 7 [6] 0 8 4 9 2 10 5 11 1 12 6 13 3 14 7(15) [7] 0(16) 8 4 9 2 10 5 11 1 12 6 13 3 14 7 15 [8] 0 16 8(17) 4 9 2 10 5 11 1 12 6 13 3 14 7 15 [9] 0 16 8 17 4(18) 9 2 10 5 11 1 12 6 13 3 14 7 15 [1] 0 16 8 17 4 18 9(19) 2 10 5 11 1 12 6 13 3 14 7 15 [2] 0 16 8 17 4 18 9 19 2(20)10 5 11 1 12 6 13 3 14 7 15 [3] 0 16 8 17 4 18 9 19 2 20 10(21) 5 11 1 12 6 13 3 14 7 15 [4] 0 16 8 17 4 18 9 19 2 20 10 21 5(22)11 1 12 6 13 3 14 7 15 [5] 0 16 8 17 4 18(19) 2 20 10 21 5 22 11 1 12 6 13 3 14 7 15 [6] 0 16 8 17 4 18 19 2(24)20 10 21 5 22 11 1 12 6 13 3 14 7 15 [7] 0 16 8 17 4 18 19 2 24 20(25)10 21 5 22 11 1 12 6 13 3 14 7 15 The goal is to be the player with the highest score after the last marble is used up. Assuming the example above ends after the marble numbered 25, the winning score is 23+9=32 (because player 5 kept marble 23 and removed marble 9, while no other player got any points in this very short example game). Here are a few more examples: 10 players; last marble is worth 1618 points: high score is 8317 13 players; last marble is worth 7999 points: high score is 146373 17 players; last marble is worth 1104 points: high score is 2764 21 players; last marble is worth 6111 points: high score is 54718 30 players; last marble is worth 5807 points: high score is 37305 What is the winning Elf's score? Your puzzle answer was 437654. --- Part Two --- Amused by the speed of your answer, the Elves are curious: What would the new winning Elf's score be if the number of the last marble were 100 times larger?	82
--- Day 13: Care Package --- As you ponder the solitude of space and the ever-increasing three-hour roundtrip for messages between you and Earth, you notice that the Space Mail Indicator Light is blinking. To help keep you sane, the Elves have sent you a care package. It's a new game for the ship's arcade cabinet! Unfortunately, the arcade is all the way on the other end of the ship. Surely, it won't be hard to build your own - the care package even comes with schematics. The arcade cabinet runs Intcode software like the game the Elves sent (your puzzle input). It has a primitive screen capable of drawing square tiles on a grid. The software draws tiles to the screen with output instructions: every three output instructions specify the x position (distance from the left), y position (distance from the top), and tile id. The tile id is interpreted as follows: 0 is an empty tile. No game object appears in this tile. 1 is a wall tile. Walls are indestructible barriers. 2 is a block tile. Blocks can be broken by the ball. 3 is a horizontal paddle tile. The paddle is indestructible. 4 is a ball tile. The ball moves diagonally and bounces off objects. For example, a sequence of output values like 1,2,3,6,5,4 would draw a horizontal paddle tile (1 tile from the left and 2 tiles from the top) and a ball tile (6 tiles from the left and 5 tiles from the top). Start the game. How many block tiles are on the screen when the game exits?	83
--- Day 18: Lavaduct Lagoon --- Thanks to your efforts, the machine parts factory is one of the first factories up and running since the lavafall came back. However, to catch up with the large backlog of parts requests, the factory will also need a large supply of lava for a while; the Elves have already started creating a large lagoon nearby for this purpose. However, they aren't sure the lagoon will be big enough; they've asked you to take a look at the dig plan (your puzzle input). For example: R 6 (#70c710) D 5 (#0dc571) L 2 (#5713f0) D 2 (#d2c081) R 2 (#59c680) D 2 (#411b91) L 5 (#8ceee2) U 2 (#caa173) L 1 (#1b58a2) U 2 (#caa171) R 2 (#7807d2) U 3 (#a77fa3) L 2 (#015232) U 2 (#7a21e3) The digger starts in a 1 meter cube hole in the ground. They then dig the specified number of meters up (U), down (D), left (L), or right (R), clearing full 1 meter cubes as they go. The directions are given as seen from above, so if "up" were north, then "right" would be east, and so on. Each trench is also listed with the color that the edge of the trench should be painted as an RGB hexadecimal color code. When viewed from above, the above example dig plan would result in the following loop of trench (#) having been dug out from otherwise ground-level terrain (.): ####### #.....# ###...# ..#...# ..#...# ###.### #...#.. ##..### .#....# .###### At this point, the trench could contain 38 cubic meters of lava. However, this is just the edge of the lagoon; the next step is to dig out the interior so that it is one meter deep as well: ####### ####### ####### ..##### ..##### ####### #####.. ####### .###### .###### Now, the lagoon can contain a much more respectable 62 cubic meters of lava. While the interior is dug out, the edges are also painted according to the color codes in the dig plan. The Elves are concerned the lagoon won't be large enough; if they follow their dig plan, how many cubic meters of lava could it hold? Your puzzle answer was 58550. --- Part Two --- The Elves were right to be concerned; the planned lagoon would be much too small. After a few minutes, someone realizes what happened; someone swapped the color and instruction parameters when producing the dig plan. They don't have time to fix the bug; one of them asks if you can extract the correct instructions from the hexadecimal codes. Each hexadecimal code is six hexadecimal digits long. The first five hexadecimal digits encode the distance in meters as a five-digit hexadecimal number. The last hexadecimal digit encodes the direction to dig: 0 means R, 1 means D, 2 means L, and 3 means U. So, in the above example, the hexadecimal codes can be converted into the true instructions: #70c710 = R 461937 #0dc571 = D 56407 #5713f0 = R 356671 #d2c081 = D 863240 #59c680 = R 367720 #411b91 = D 266681 #8ceee2 = L 577262 #caa173 = U 829975 #1b58a2 = L 112010 #caa171 = D 829975 #7807d2 = L 491645 #a77fa3 = U 686074 #015232 = L 5411 #7a21e3 = U 500254 Digging out this loop and its interior produces a lagoon that can hold an impressive 952408144115 cubic meters of lava. Convert the hexadecimal color codes into the correct instructions; if the Elves follow this new dig plan, how many cubic meters of lava could the lagoon hold?	84
--- Day 19: An Elephant Named Joseph --- The Elves contact you over a highly secure emergency channel. Back at the North Pole, the Elves are busy misunderstanding White Elephant parties. Each Elf brings a present. They all sit in a circle, numbered starting with position 1. Then, starting with the first Elf, they take turns stealing all the presents from the Elf to their left. An Elf with no presents is removed from the circle and does not take turns. For example, with five Elves (numbered 1 to 5): 1 5 2 4 3 Elf 1 takes Elf 2's present. Elf 2 has no presents and is skipped. Elf 3 takes Elf 4's present. Elf 4 has no presents and is also skipped. Elf 5 takes Elf 1's two presents. Neither Elf 1 nor Elf 2 have any presents, so both are skipped. Elf 3 takes Elf 5's three presents. So, with five Elves, the Elf that sits starting in position 3 gets all the presents. With the number of Elves given in your puzzle input, which Elf gets all the presents?	85
--- Day 1: Historian Hysteria --- The Chief Historian is always present for the big Christmas sleigh launch, but nobody has seen him in months! Last anyone heard, he was visiting locations that are historically significant to the North Pole; a group of Senior Historians has asked you to accompany them as they check the places they think he was most likely to visit. As each location is checked, they will mark it on their list with a star. They figure the Chief Historian must be in one of the first fifty places they'll look, so in order to save Christmas, you need to help them get fifty stars on their list before Santa takes off on December 25th. Collect stars by solving puzzles. Two puzzles will be made available on each day in the Advent calendar; the second puzzle is unlocked when you complete the first. Each puzzle grants one star. Good luck! You haven't even left yet and the group of Elvish Senior Historians has already hit a problem: their list of locations to check is currently empty. Eventually, someone decides that the best place to check first would be the Chief Historian's office. Upon pouring into the office, everyone confirms that the Chief Historian is indeed nowhere to be found. Instead, the Elves discover an assortment of notes and lists of historically significant locations! This seems to be the planning the Chief Historian was doing before he left. Perhaps these notes can be used to determine which locations to search? Throughout the Chief's office, the historically significant locations are listed not by name but by a unique number called the location ID. To make sure they don't miss anything, The Historians split into two groups, each searching the office and trying to create their own complete list of location IDs. There's just one problem: by holding the two lists up side by side (your puzzle input), it quickly becomes clear that the lists aren't very similar. Maybe you can help The Historians reconcile their lists? For example: 3 4 4 3 2 5 1 3 3 9 3 3 Maybe the lists are only off by a small amount! To find out, pair up the numbers and measure how far apart they are. Pair up the smallest number in the left list with the smallest number in the right list, then the second-smallest left number with the second-smallest right number, and so on. Within each pair, figure out how far apart the two numbers are; you'll need to add up all of those distances. For example, if you pair up a 3 from the left list with a 7 from the right list, the distance apart is 4; if you pair up a 9 with a 3, the distance apart is 6. In the example list above, the pairs and distances would be as follows: The smallest number in the left list is 1, and the smallest number in the right list is 3. The distance between them is 2. The second-smallest number in the left list is 2, and the second-smallest number in the right list is another 3. The distance between them is 1. The third-smallest number in both lists is 3, so the distance between them is 0. The next numbers to pair up are 3 and 4, a distance of 1. The fifth-smallest numbers in each list are 3 and 5, a distance of 2. Finally, the largest number in the left list is 4, while the largest number in the right list is 9; these are a distance 5 apart. To find the total distance between the left list and the right list, add up the distances between all of the pairs you found. In the example above, this is 2 + 1 + 0 + 1 + 2 + 5, a total distance of 11! Your actual left and right lists contain many location IDs. What is the total distance between your lists?	86
--- Day 11: Plutonian Pebbles --- The ancient civilization on Pluto was known for its ability to manipulate spacetime, and while The Historians explore their infinite corridors, you've noticed a strange set of physics-defying stones. At first glance, they seem like normal stones: they're arranged in a perfectly straight line, and each stone has a number engraved on it. The strange part is that every time you blink, the stones change. Sometimes, the number engraved on a stone changes. Other times, a stone might split in two, causing all the other stones to shift over a bit to make room in their perfectly straight line. As you observe them for a while, you find that the stones have a consistent behavior. Every time you blink, the stones each simultaneously change according to the first applicable rule in this list: If the stone is engraved with the number 0, it is replaced by a stone engraved with the number 1. If the stone is engraved with a number that has an even number of digits, it is replaced by two stones. The left half of the digits are engraved on the new left stone, and the right half of the digits are engraved on the new right stone. (The new numbers don't keep extra leading zeroes: 1000 would become stones 10 and 0.) If none of the other rules apply, the stone is replaced by a new stone; the old stone's number multiplied by 2024 is engraved on the new stone. No matter how the stones change, their order is preserved, and they stay on their perfectly straight line. How will the stones evolve if you keep blinking at them? You take a note of the number engraved on each stone in the line (your puzzle input). If you have an arrangement of five stones engraved with the numbers 0 1 10 99 999 and you blink once, the stones transform as follows: The first stone, 0, becomes a stone marked 1. The second stone, 1, is multiplied by 2024 to become 2024. The third stone, 10, is split into a stone marked 1 followed by a stone marked 0. The fourth stone, 99, is split into two stones marked 9. The fifth stone, 999, is replaced by a stone marked 2021976. So, after blinking once, your five stones would become an arrangement of seven stones engraved with the numbers 1 2024 1 0 9 9 2021976. Here is a longer example: Initial arrangement: 125 17 After 1 blink: 253000 1 7 After 2 blinks: 253 0 2024 14168 After 3 blinks: 512072 1 20 24 28676032 After 4 blinks: 512 72 2024 2 0 2 4 2867 6032 After 5 blinks: 1036288 7 2 20 24 4048 1 4048 8096 28 67 60 32 After 6 blinks: 2097446912 14168 4048 2 0 2 4 40 48 2024 40 48 80 96 2 8 6 7 6 0 3 2 In this example, after blinking six times, you would have 22 stones. After blinking 25 times, you would have 55312 stones! Consider the arrangement of stones in front of you. How many stones will you have after blinking 25 times? Your puzzle answer was 211306. The first half of this puzzle is complete! It provides one gold star: * --- Part Two --- The Historians sure are taking a long time. To be fair, the infinite corridors are very large. How many stones would you have after blinking a total of 75 times?	87
--- Day 10: Hoof It --- You all arrive at a Lava Production Facility on a floating island in the sky. As the others begin to search the massive industrial complex, you feel a small nose boop your leg and look down to discover a reindeer wearing a hard hat. The reindeer is holding a book titled "Lava Island Hiking Guide". However, when you open the book, you discover that most of it seems to have been scorched by lava! As you're about to ask how you can help, the reindeer brings you a blank topographic map of the surrounding area (your puzzle input) and looks up at you excitedly. Perhaps you can help fill in the missing hiking trails? The topographic map indicates the height at each position using a scale from 0 (lowest) to 9 (highest). For example: 0123 1234 8765 9876 Based on un-scorched scraps of the book, you determine that a good hiking trail is as long as possible and has an even, gradual, uphill slope. For all practical purposes, this means that a hiking trail is any path that starts at height 0, ends at height 9, and always increases by a height of exactly 1 at each step. Hiking trails never include diagonal steps - only up, down, left, or right (from the perspective of the map). You look up from the map and notice that the reindeer has helpfully begun to construct a small pile of pencils, markers, rulers, compasses, stickers, and other equipment you might need to update the map with hiking trails. A trailhead is any position that starts one or more hiking trails - here, these positions will always have height 0. Assembling more fragments of pages, you establish that a trailhead's score is the number of 9-height positions reachable from that trailhead via a hiking trail. In the above example, the single trailhead in the top left corner has a score of 1 because it can reach a single 9 (the one in the bottom left). This trailhead has a score of 2: ...0... ...1... ...2... 6543456 7.....7 8.....8 9.....9 (The positions marked . are impassable tiles to simplify these examples; they do not appear on your actual topographic map.) This trailhead has a score of 4 because every 9 is reachable via a hiking trail except the one immediately to the left of the trailhead: ..90..9 ...1.98 ...2..7 6543456 765.987 876.... 987.... This topographic map contains two trailheads; the trailhead at the top has a score of 1, while the trailhead at the bottom has a score of 2: 10..9.. 2...8.. 3...7.. 4567654 ...8..3 ...9..2 .....01 Here's a larger example: 89010123 78121874 87430965 96549874 45678903 32019012 01329801 10456732 This larger example has 9 trailheads. Considering the trailheads in reading order, they have scores of 5, 6, 5, 3, 1, 3, 5, 3, and 5. Adding these scores together, the sum of the scores of all trailheads is 36. The reindeer gleefully carries over a protractor and adds it to the pile. What is the sum of the scores of all trailheads on your topographic map?	88
--- Day 5: Hydrothermal Venture --- You come across a field of hydrothermal vents on the ocean floor! These vents constantly produce large, opaque clouds, so it would be best to avoid them if possible. They tend to form in lines; the submarine helpfully produces a list of nearby lines of vents (your puzzle input) for you to review. For example: 0,9 -> 5,9 8,0 -> 0,8 9,4 -> 3,4 2,2 -> 2,1 7,0 -> 7,4 6,4 -> 2,0 0,9 -> 2,9 3,4 -> 1,4 0,0 -> 8,8 5,5 -> 8,2 Each line of vents is given as a line segment in the format x1,y1 -> x2,y2 where x1,y1 are the coordinates of one end the line segment and x2,y2 are the coordinates of the other end. These line segments include the points at both ends. In other words: An entry like 1,1 -> 1,3 covers points 1,1, 1,2, and 1,3. An entry like 9,7 -> 7,7 covers points 9,7, 8,7, and 7,7. For now, only consider horizontal and vertical lines: lines where either x1 = x2 or y1 = y2. So, the horizontal and vertical lines from the above list would produce the following diagram: .......1.. ..1....1.. ..1....1.. .......1.. .112111211 .......... .......... .......... .......... 222111.... In this diagram, the top left corner is 0,0 and the bottom right corner is 9,9. Each position is shown as the number of lines which cover that point or . if no line covers that point. The top-left pair of 1s, for example, comes from 2,2 -> 2,1; the very bottom row is formed by the overlapping lines 0,9 -> 5,9 and 0,9 -> 2,9. To avoid the most dangerous areas, you need to determine the number of points where at least two lines overlap. In the above example, this is anywhere in the diagram with a 2 or larger - a total of 5 points. Consider only horizontal and vertical lines. At how many points do at least two lines overlap?	89
--- Day 6: Tuning Trouble --- The preparations are finally complete; you and the Elves leave camp on foot and begin to make your way toward the star fruit grove. As you move through the dense undergrowth, one of the Elves gives you a handheld device. He says that it has many fancy features, but the most important one to set up right now is the communication system. However, because he's heard you have significant experience dealing with signal-based systems, he convinced the other Elves that it would be okay to give you their one malfunctioning device - surely you'll have no problem fixing it. As if inspired by comedic timing, the device emits a few colorful sparks. To be able to communicate with the Elves, the device needs to lock on to their signal. The signal is a series of seemingly-random characters that the device receives one at a time. To fix the communication system, you need to add a subroutine to the device that detects a start-of-packet marker in the datastream. In the protocol being used by the Elves, the start of a packet is indicated by a sequence of four characters that are all different. The device will send your subroutine a datastream buffer (your puzzle input); your subroutine needs to identify the first position where the four most recently received characters were all different. Specifically, it needs to report the number of characters from the beginning of the buffer to the end of the first such four-character marker. For example, suppose you receive the following datastream buffer: mjqjpqmgbljsphdztnvjfqwrcgsmlb After the first three characters (mjq) have been received, there haven't been enough characters received yet to find the marker. The first time a marker could occur is after the fourth character is received, making the most recent four characters mjqj. Because j is repeated, this isn't a marker. The first time a marker appears is after the seventh character arrives. Once it does, the last four characters received are jpqm, which are all different. In this case, your subroutine should report the value 7, because the first start-of-packet marker is complete after 7 characters have been processed. Here are a few more examples: bvwbjplbgvbhsrlpgdmjqwftvncz: first marker after character 5 nppdvjthqldpwncqszvftbrmjlhg: first marker after character 6 nznrnfrfntjfmvfwmzdfjlvtqnbhcprsg: first marker after character 10 zcfzfwzzqfrljwzlrfnpqdbhtmscgvjw: first marker after character 11 How many characters need to be processed before the first start-of-packet marker is detected?	90
--- Day 19: Beacon Scanner --- As your probe drifted down through this area, it released an assortment of beacons and scanners into the water. It's difficult to navigate in the pitch black open waters of the ocean trench, but if you can build a map of the trench using data from the scanners, you should be able to safely reach the bottom. The beacons and scanners float motionless in the water; they're designed to maintain the same position for long periods of time. Each scanner is capable of detecting all beacons in a large cube centered on the scanner; beacons that are at most 1000 units away from the scanner in each of the three axes (x, y, and z) have their precise position determined relative to the scanner. However, scanners cannot detect other scanners. The submarine has automatically summarized the relative positions of beacons detected by each scanner (your puzzle input). For example, if a scanner is at x,y,z coordinates 500,0,-500 and there are beacons at -500,1000,-1500 and 1501,0,-500, the scanner could report that the first beacon is at -1000,1000,-1000 (relative to the scanner) but would not detect the second beacon at all. Unfortunately, while each scanner can report the positions of all detected beacons relative to itself, the scanners do not know their own position. You'll need to determine the positions of the beacons and scanners yourself. The scanners and beacons map a single contiguous 3d region. This region can be reconstructed by finding pairs of scanners that have overlapping detection regions such that there are at least 12 beacons that both scanners detect within the overlap. By establishing 12 common beacons, you can precisely determine where the scanners are relative to each other, allowing you to reconstruct the beacon map one scanner at a time. For a moment, consider only two dimensions. Suppose you have the following scanner reports: --- scanner 0 --- 0,2 4,1 3,3 --- scanner 1 --- -1,-1 -5,0 -2,1 Drawing x increasing rightward, y increasing upward, scanners as S, and beacons as B, scanner 0 detects this: ...B. B.... ....B S.... Scanner 1 detects this: ...B.. B....S ....B. For this example, assume scanners only need 3 overlapping beacons. Then, the beacons visible to both scanners overlap to produce the following complete map: ...B.. B....S ....B. S..... Unfortunately, there's a second problem: the scanners also don't know their rotation or facing direction. Due to magnetic alignment, each scanner is rotated some integer number of 90-degree turns around all of the x, y, and z axes. That is, one scanner might call a direction positive x, while another scanner might call that direction negative y. Or, two scanners might agree on which direction is positive x, but one scanner might be upside-down from the perspective of the other scanner. In total, each scanner could be in any of 24 different orientations: facing positive or negative x, y, or z, and considering any of four directions "up" from that facing. For example, here is an arrangement of beacons as seen from a scanner in the same position but in different orientations: --- scanner 0 --- -1,-1,1 -2,-2,2 -3,-3,3 -2,-3,1 5,6,-4 8,0,7 --- scanner 0 --- 1,-1,1 2,-2,2 3,-3,3 2,-1,3 -5,4,-6 -8,-7,0 --- scanner 0 --- -1,-1,-1 -2,-2,-2 -3,-3,-3 -1,-3,-2 4,6,5 -7,0,8 --- scanner 0 --- 1,1,-1 2,2,-2 3,3,-3 1,3,-2 -4,-6,5 7,0,8 --- scanner 0 --- 1,1,1 2,2,2 3,3,3 3,1,2 -6,-4,-5 0,7,-8 By finding pairs of scanners that both see at least 12 of the same beacons, you can assemble the entire map. For example, consider the following report: --- scanner 0 --- 404,-588,-901 528,-643,409 -838,591,734 390,-675,-793 -537,-823,-458 -485,-357,347 -345,-311,381 -661,-816,-575 -876,649,763 -618,-824,-621 553,345,-567 474,580,667 -447,-329,318 -584,868,-557 544,-627,-890 564,392,-477 455,729,728 -892,524,684 -689,845,-530 423,-701,434 7,-33,-71 630,319,-379 443,580,662 -789,900,-551 459,-707,401 --- scanner 1 --- 686,422,578 605,423,415 515,917,-361 -336,658,858 95,138,22 -476,619,847 -340,-569,-846 567,-361,727 -460,603,-452 669,-402,600 729,430,532 -500,-761,534 -322,571,750 -466,-666,-811 -429,-592,574 -355,545,-477 703,-491,-529 -328,-685,520 413,935,-424 -391,539,-444 586,-435,557 -364,-763,-893 807,-499,-711 755,-354,-619 553,889,-390 --- scanner 2 --- 649,640,665 682,-795,504 -784,533,-524 -644,584,-595 -588,-843,648 -30,6,44 -674,560,763 500,723,-460 609,671,-379 -555,-800,653 -675,-892,-343 697,-426,-610 578,704,681 493,664,-388 -671,-858,530 -667,343,800 571,-461,-707 -138,-166,112 -889,563,-600 646,-828,498 640,759,510 -630,509,768 -681,-892,-333 673,-379,-804 -742,-814,-386 577,-820,562 --- scanner 3 --- -589,542,597 605,-692,669 -500,565,-823 -660,373,557 -458,-679,-417 -488,449,543 -626,468,-788 338,-750,-386 528,-832,-391 562,-778,733 -938,-730,414 543,643,-506 -524,371,-870 407,773,750 -104,29,83 378,-903,-323 -778,-728,485 426,699,580 -438,-605,-362 -469,-447,-387 509,732,623 647,635,-688 -868,-804,481 614,-800,639 595,780,-596 --- scanner 4 --- 727,592,562 -293,-554,779 441,611,-461 -714,465,-776 -743,427,-804 -660,-479,-426 832,-632,460 927,-485,-438 408,393,-506 466,436,-512 110,16,151 -258,-428,682 -393,719,612 -211,-452,876 808,-476,-593 -575,615,604 -485,667,467 -680,325,-822 -627,-443,-432 872,-547,-609 833,512,582 807,604,487 839,-516,451 891,-625,532 -652,-548,-490 30,-46,-14 Because all coordinates are relative, in this example, all "absolute" positions will be expressed relative to scanner 0 (using the orientation of scanner 0 and as if scanner 0 is at coordinates 0,0,0). Scanners 0 and 1 have overlapping detection cubes; the 12 beacons they both detect (relative to scanner 0) are at the following coordinates: -618,-824,-621 -537,-823,-458 -447,-329,318 404,-588,-901 544,-627,-890 528,-643,409 -661,-816,-575 390,-675,-793 423,-701,434 -345,-311,381 459,-707,401 -485,-357,347 These same 12 beacons (in the same order) but from the perspective of scanner 1 are: 686,422,578 605,423,415 515,917,-361 -336,658,858 -476,619,847 -460,603,-452 729,430,532 -322,571,750 -355,545,-477 413,935,-424 -391,539,-444 553,889,-390 Because of this, scanner 1 must be at 68,-1246,-43 (relative to scanner 0). Scanner 4 overlaps with scanner 1; the 12 beacons they both detect (relative to scanner 0) are: 459,-707,401 -739,-1745,668 -485,-357,347 432,-2009,850 528,-643,409 423,-701,434 -345,-311,381 408,-1815,803 534,-1912,768 -687,-1600,576 -447,-329,318 -635,-1737,486 So, scanner 4 is at -20,-1133,1061 (relative to scanner 0). Following this process, scanner 2 must be at 1105,-1205,1229 (relative to scanner 0) and scanner 3 must be at -92,-2380,-20 (relative to scanner 0). The full list of beacons (relative to scanner 0) is: -892,524,684 -876,649,763 -838,591,734 -789,900,-551 -739,-1745,668 -706,-3180,-659 -697,-3072,-689 -689,845,-530 -687,-1600,576 -661,-816,-575 -654,-3158,-753 -635,-1737,486 -631,-672,1502 -624,-1620,1868 -620,-3212,371 -618,-824,-621 -612,-1695,1788 -601,-1648,-643 -584,868,-557 -537,-823,-458 -532,-1715,1894 -518,-1681,-600 -499,-1607,-770 -485,-357,347 -470,-3283,303 -456,-621,1527 -447,-329,318 -430,-3130,366 -413,-627,1469 -345,-311,381 -36,-1284,1171 -27,-1108,-65 7,-33,-71 12,-2351,-103 26,-1119,1091 346,-2985,342 366,-3059,397 377,-2827,367 390,-675,-793 396,-1931,-563 404,-588,-901 408,-1815,803 423,-701,434 432,-2009,850 443,580,662 455,729,728 456,-540,1869 459,-707,401 465,-695,1988 474,580,667 496,-1584,1900 497,-1838,-617 527,-524,1933 528,-643,409 534,-1912,768 544,-627,-890 553,345,-567 564,392,-477 568,-2007,-577 605,-1665,1952 612,-1593,1893 630,319,-379 686,-3108,-505 776,-3184,-501 846,-3110,-434 1135,-1161,1235 1243,-1093,1063 1660,-552,429 1693,-557,386 1735,-437,1738 1749,-1800,1813 1772,-405,1572 1776,-675,371 1779,-442,1789 1780,-1548,337 1786,-1538,337 1847,-1591,415 1889,-1729,1762 1994,-1805,1792 In total, there are 79 beacons. Assemble the full map of beacons. How many beacons are there? Your puzzle answer was 432. --- Part Two --- Sometimes, it's a good idea to appreciate just how big the ocean is. Using the Manhattan distance, how far apart do the scanners get? In the above example, scanners 2 (1105,-1205,1229) and 3 (-92,-2380,-20) are the largest Manhattan distance apart. In total, they are 1197 + 1175 + 1249 = 3621 units apart. What is the largest Manhattan distance between any two scanners?	91
--- Day 19: Linen Layout --- Today, The Historians take you up to the hot springs on Gear Island! Very suspiciously, absolutely nothing goes wrong as they begin their careful search of the vast field of helixes. Could this finally be your chance to visit the onsen next door? Only one way to find out. After a brief conversation with the reception staff at the onsen front desk, you discover that you don't have the right kind of money to pay the admission fee. However, before you can leave, the staff get your attention. Apparently, they've heard about how you helped at the hot springs, and they're willing to make a deal: if you can simply help them arrange their towels, they'll let you in for free! Every towel at this onsen is marked with a pattern of colored stripes. There are only a few patterns, but for any particular pattern, the staff can get you as many towels with that pattern as you need. Each stripe can be white (w), blue (u), black (b), red (r), or green (g). So, a towel with the pattern ggr would have a green stripe, a green stripe, and then a red stripe, in that order. (You can't reverse a pattern by flipping a towel upside-down, as that would cause the onsen logo to face the wrong way.) The Official Onsen Branding Expert has produced a list of designs - each a long sequence of stripe colors - that they would like to be able to display. You can use any towels you want, but all of the towels' stripes must exactly match the desired design. So, to display the design rgrgr, you could use two rg towels and then an r towel, an rgr towel and then a gr towel, or even a single massive rgrgr towel (assuming such towel patterns were actually available). To start, collect together all of the available towel patterns and the list of desired designs (your puzzle input). For example: r, wr, b, g, bwu, rb, gb, br brwrr bggr gbbr rrbgbr ubwu bwurrg brgr bbrgwb The first line indicates the available towel patterns; in this example, the onsen has unlimited towels with a single red stripe (r), unlimited towels with a white stripe and then a red stripe (wr), and so on. After the blank line, the remaining lines each describe a design the onsen would like to be able to display. In this example, the first design (brwrr) indicates that the onsen would like to be able to display a black stripe, a red stripe, a white stripe, and then two red stripes, in that order. Not all designs will be possible with the available towels. In the above example, the designs are possible or impossible as follows: brwrr can be made with a br towel, then a wr towel, and then finally an r towel. bggr can be made with a b towel, two g towels, and then an r towel. gbbr can be made with a gb towel and then a br towel. rrbgbr can be made with r, rb, g, and br. ubwu is impossible. bwurrg can be made with bwu, r, r, and g. brgr can be made with br, g, and r. bbrgwb is impossible. In this example, 6 of the eight designs are possible with the available towel patterns. To get into the onsen as soon as possible, consult your list of towel patterns and desired designs carefully. How many designs are possible? Your puzzle answer was 304. The first half of this puzzle is complete! It provides one gold star: * --- Part Two --- The staff don't really like some of the towel arrangements you came up with. To avoid an endless cycle of towel rearrangement, maybe you should just give them every possible option. Here are all of the different ways the above example's designs can be made: brwrr can be made in two different ways: b, r, wr, r or br, wr, r. bggr can only be made with b, g, g, and r. gbbr can be made 4 different ways: g, b, b, r g, b, br gb, b, r gb, br rrbgbr can be made 6 different ways: r, r, b, g, b, r r, r, b, g, br r, r, b, gb, r r, rb, g, b, r r, rb, g, br r, rb, gb, r bwurrg can only be made with bwu, r, r, and g. brgr can be made in two different ways: b, r, g, r or br, g, r. ubwu and bbrgwb are still impossible. Adding up all of the ways the towels in this example could be arranged into the desired designs yields 16 (2 + 1 + 4 + 6 + 1 + 2). They'll let you into the onsen as soon as you have the list. What do you get if you add up the number of different ways you could make each design?	92
--- Day 11: Hex Ed --- Crossing the bridge, you've barely reached the other side of the stream when a program comes up to you, clearly in distress. "It's my child process," she says, "he's gotten lost in an infinite grid!" Fortunately for her, you have plenty of experience with infinite grids. Unfortunately for you, it's a hex grid. The hexagons ("hexes") in this grid are aligned such that adjacent hexes can be found to the north, northeast, southeast, south, southwest, and northwest: n / nw +--+ ne / -+ +- / sw +--+ se / s You have the path the child process took. Starting where he started, you need to determine the fewest number of steps required to reach him. (A "step" means to move from the hex you are in to any adjacent hex.) For example: ne,ne,ne is 3 steps away. ne,ne,sw,sw is 0 steps away (back where you started). ne,ne,s,s is 2 steps away (se,se). se,sw,se,sw,sw is 3 steps away (s,s,sw).	93
--- Day 8: Space Image Format --- The Elves' spirits are lifted when they realize you have an opportunity to reboot one of their Mars rovers, and so they are curious if you would spend a brief sojourn on Mars. You land your ship near the rover. When you reach the rover, you discover that it's already in the process of rebooting! It's just waiting for someone to enter a BIOS password. The Elf responsible for the rover takes a picture of the password (your puzzle input) and sends it to you via the Digital Sending Network. Unfortunately, images sent via the Digital Sending Network aren't encoded with any normal encoding; instead, they're encoded in a special Space Image Format. None of the Elves seem to remember why this is the case. They send you the instructions to decode it. Images are sent as a series of digits that each represent the color of a single pixel. The digits fill each row of the image left-to-right, then move downward to the next row, filling rows top-to-bottom until every pixel of the image is filled. Each image actually consists of a series of identically-sized layers that are filled in this way. So, the first digit corresponds to the top-left pixel of the first layer, the second digit corresponds to the pixel to the right of that on the same layer, and so on until the last digit, which corresponds to the bottom-right pixel of the last layer. For example, given an image 3 pixels wide and 2 pixels tall, the image data 123456789012 corresponds to the following image layers: Layer 1: 123 456 Layer 2: 789 012 The image you received is 25 pixels wide and 6 pixels tall. To make sure the image wasn't corrupted during transmission, the Elves would like you to find the layer that contains the fewest 0 digits. On that layer, what is the number of 1 digits multiplied by the number of 2 digits?	94
--- Day 17: Pyroclastic Flow --- Your handheld device has located an alternative exit from the cave for you and the elephants. The ground is rumbling almost continuously now, but the strange valves bought you some time. It's definitely getting warmer in here, though. The tunnels eventually open into a very tall, narrow chamber. Large, oddly-shaped rocks are falling into the chamber from above, presumably due to all the rumbling. If you can't work out where the rocks will fall next, you might be crushed! The five types of rocks have the following peculiar shapes, where # is rock and . is empty space: #### .#. ### .#. ..# ..# ### # # # # ## ## The rocks fall in the order shown above: first the - shape, then the + shape, and so on. Once the end of the list is reached, the same order repeats: the - shape falls first, sixth, 11th, 16th, etc. The rocks don't spin, but they do get pushed around by jets of hot gas coming out of the walls themselves. A quick scan reveals the effect the jets of hot gas will have on the rocks as they fall (your puzzle input). For example, suppose this was the jet pattern in your cave: >>><<><>><<<>><>>><<<>>><<<><<<>><>><<>> In jet patterns, < means a push to the left, while > means a push to the right. The pattern above means that the jets will push a falling rock right, then right, then right, then left, then left, then right, and so on. If the end of the list is reached, it repeats. The tall, vertical chamber is exactly seven units wide. Each rock appears so that its left edge is two units away from the left wall and its bottom edge is three units above the highest rock in the room (or the floor, if there isn't one). After a rock appears, it alternates between being pushed by a jet of hot gas one unit (in the direction indicated by the next symbol in the jet pattern) and then falling one unit down. If any movement would cause any part of the rock to move into the walls, floor, or a stopped rock, the movement instead does not occur. If a downward movement would have caused a falling rock to move into the floor or an already-fallen rock, the falling rock stops where it is (having landed on something) and a new rock immediately begins falling. Drawing falling rocks with @ and stopped rocks with #, the jet pattern in the example above manifests as follows: The first rock begins falling: \|..@@@@.\| \|.......\| \|.......\| \|.......\| +-------+ Jet of gas pushes rock right: \|...@@@@\| \|.......\| \|.......\| \|.......\| +-------+ Rock falls 1 unit: \|...@@@@\| \|.......\| \|.......\| +-------+ Jet of gas pushes rock right, but nothing happens: \|...@@@@\| \|.......\| \|.......\| +-------+ Rock falls 1 unit: \|...@@@@\| \|.......\| +-------+ Jet of gas pushes rock right, but nothing happens: \|...@@@@\| \|.......\| +-------+ Rock falls 1 unit: \|...@@@@\| +-------+ Jet of gas pushes rock left: \|..@@@@.\| +-------+ Rock falls 1 unit, causing it to come to rest: \|..####.\| +-------+ A new rock begins falling: \|...@...\| \|..@@@..\| \|...@...\| \|.......\| \|.......\| \|.......\| \|..####.\| +-------+ Jet of gas pushes rock left: \|..@....\| \|.@@@...\| \|..@....\| \|.......\| \|.......\| \|.......\| \|..####.\| +-------+ Rock falls 1 unit: \|..@....\| \|.@@@...\| \|..@....\| \|.......\| \|.......\| \|..####.\| +-------+ Jet of gas pushes rock right: \|...@...\| \|..@@@..\| \|...@...\| \|.......\| \|.......\| \|..####.\| +-------+ Rock falls 1 unit: \|...@...\| \|..@@@..\| \|...@...\| \|.......\| \|..####.\| +-------+ Jet of gas pushes rock left: \|..@....\| \|.@@@...\| \|..@....\| \|.......\| \|..####.\| +-------+ Rock falls 1 unit: \|..@....\| \|.@@@...\| \|..@....\| \|..####.\| +-------+ Jet of gas pushes rock right: \|...@...\| \|..@@@..\| \|...@...\| \|..####.\| +-------+ Rock falls 1 unit, causing it to come to rest: \|...#...\| \|..###..\| \|...#...\| \|..####.\| +-------+ A new rock begins falling: \|....@..\| \|....@..\| \|..@@@..\| \|.......\| \|.......\| \|.......\| \|...#...\| \|..###..\| \|...#...\| \|..####.\| +-------+ The moment each of the next few rocks begins falling, you would see this: \|..@....\| \|..@....\| \|..@....\| \|..@....\| \|.......\| \|.......\| \|.......\| \|..#....\| \|..#....\| \|####...\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|..@@...\| \|..@@...\| \|.......\| \|.......\| \|.......\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|..@@@@.\| \|.......\| \|.......\| \|.......\| \|....##.\| \|....##.\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|...@...\| \|..@@@..\| \|...@...\| \|.......\| \|.......\| \|.......\| \|.####..\| \|....##.\| \|....##.\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|....@..\| \|....@..\| \|..@@@..\| \|.......\| \|.......\| \|.......\| \|..#....\| \|.###...\| \|..#....\| \|.####..\| \|....##.\| \|....##.\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|..@....\| \|..@....\| \|..@....\| \|..@....\| \|.......\| \|.......\| \|.......\| \|.....#.\| \|.....#.\| \|..####.\| \|.###...\| \|..#....\| \|.####..\| \|....##.\| \|....##.\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|..@@...\| \|..@@...\| \|.......\| \|.......\| \|.......\| \|....#..\| \|....#..\| \|....##.\| \|....##.\| \|..####.\| \|.###...\| \|..#....\| \|.####..\| \|....##.\| \|....##.\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ \|..@@@@.\| \|.......\| \|.......\| \|.......\| \|....#..\| \|....#..\| \|....##.\| \|##..##.\| \|######.\| \|.###...\| \|..#....\| \|.####..\| \|....##.\| \|....##.\| \|....#..\| \|..#.#..\| \|..#.#..\| \|#####..\| \|..###..\| \|...#...\| \|..####.\| +-------+ To prove to the elephants your simulation is accurate, they want to know how tall the tower will get after 2022 rocks have stopped (but before the 2023rd rock begins falling). In this example, the tower of rocks will be 3068 units tall. How many units tall will the tower of rocks be after 2022 rocks have stopped falling?	95
--- Day 21: Allergen Assessment --- You reach the train's last stop and the closest you can get to your vacation island without getting wet. There aren't even any boats here, but nothing can stop you now: you build a raft. You just need a few days' worth of food for your journey. You don't speak the local language, so you can't read any ingredients lists. However, sometimes, allergens are listed in a language you do understand. You should be able to use this information to determine which ingredient contains which allergen and work out which foods are safe to take with you on your trip. You start by compiling a list of foods (your puzzle input), one food per line. Each line includes that food's ingredients list followed by some or all of the allergens the food contains. Each allergen is found in exactly one ingredient. Each ingredient contains zero or one allergen. Allergens aren't always marked; when they're listed (as in (contains nuts, shellfish) after an ingredients list), the ingredient that contains each listed allergen will be somewhere in the corresponding ingredients list. However, even if an allergen isn't listed, the ingredient that contains that allergen could still be present: maybe they forgot to label it, or maybe it was labeled in a language you don't know. For example, consider the following list of foods: mxmxvkd kfcds sqjhc nhms (contains dairy, fish) trh fvjkl sbzzf mxmxvkd (contains dairy) sqjhc fvjkl (contains soy) sqjhc mxmxvkd sbzzf (contains fish) The first food in the list has four ingredients (written in a language you don't understand): mxmxvkd, kfcds, sqjhc, and nhms. While the food might contain other allergens, a few allergens the food definitely contains are listed afterward: dairy and fish. The first step is to determine which ingredients can't possibly contain any of the allergens in any food in your list. In the above example, none of the ingredients kfcds, nhms, sbzzf, or trh can contain an allergen. Counting the number of times any of these ingredients appear in any ingredients list produces 5: they all appear once each except sbzzf, which appears twice. Determine which ingredients cannot possibly contain any of the allergens in your list. How many times do any of those ingredients appear? Your puzzle answer was 2176. --- Part Two --- Now that you've isolated the inert ingredients, you should have enough information to figure out which ingredient contains which allergen. In the above example: mxmxvkd contains dairy. sqjhc contains fish. fvjkl contains soy. Arrange the ingredients alphabetically by their allergen and separate them by commas to produce your canonical dangerous ingredient list. (There should not be any spaces in your canonical dangerous ingredient list.) In the above example, this would be mxmxvkd,sqjhc,fvjkl. Time to stock your raft with supplies. What is your canonical dangerous ingredient list?	96
--- Day 6: Wait For It --- The ferry quickly brings you across Island Island. After asking around, you discover that there is indeed normally a large pile of sand somewhere near here, but you don't see anything besides lots of water and the small island where the ferry has docked. As you try to figure out what to do next, you notice a poster on a wall near the ferry dock. "Boat races! Open to the public! Grand prize is an all-expenses-paid trip to Desert Island!" That must be where the sand comes from! Best of all, the boat races are starting in just a few minutes. You manage to sign up as a competitor in the boat races just in time. The organizer explains that it's not really a traditional race - instead, you will get a fixed amount of time during which your boat has to travel as far as it can, and you win if your boat goes the farthest. As part of signing up, you get a sheet of paper (your puzzle input) that lists the time allowed for each race and also the best distance ever recorded in that race. To guarantee you win the grand prize, you need to make sure you go farther in each race than the current record holder. The organizer brings you over to the area where the boat races are held. The boats are much smaller than you expected - they're actually toy boats, each with a big button on top. Holding down the button charges the boat, and releasing the button allows the boat to move. Boats move faster if their button was held longer, but time spent holding the button counts against the total race time. You can only hold the button at the start of the race, and boats don't move until the button is released. For example: Time: 7 15 30 Distance: 9 40 200 This document describes three races: The first race lasts 7 milliseconds. The record distance in this race is 9 millimeters. The second race lasts 15 milliseconds. The record distance in this race is 40 millimeters. The third race lasts 30 milliseconds. The record distance in this race is 200 millimeters. Your toy boat has a starting speed of zero millimeters per millisecond. For each whole millisecond you spend at the beginning of the race holding down the button, the boat's speed increases by one millimeter per millisecond. So, because the first race lasts 7 milliseconds, you only have a few options: Don't hold the button at all (that is, hold it for 0 milliseconds) at the start of the race. The boat won't move; it will have traveled 0 millimeters by the end of the race. Hold the button for 1 millisecond at the start of the race. Then, the boat will travel at a speed of 1 millimeter per millisecond for 6 milliseconds, reaching a total distance traveled of 6 millimeters. Hold the button for 2 milliseconds, giving the boat a speed of 2 millimeters per millisecond. It will then get 5 milliseconds to move, reaching a total distance of 10 millimeters. Hold the button for 3 milliseconds. After its remaining 4 milliseconds of travel time, the boat will have gone 12 millimeters. Hold the button for 4 milliseconds. After its remaining 3 milliseconds of travel time, the boat will have gone 12 millimeters. Hold the button for 5 milliseconds, causing the boat to travel a total of 10 millimeters. Hold the button for 6 milliseconds, causing the boat to travel a total of 6 millimeters. Hold the button for 7 milliseconds. That's the entire duration of the race. You never let go of the button. The boat can't move until you let go of the button. Please make sure you let go of the button so the boat gets to move. 0 millimeters. Since the current record for this race is 9 millimeters, there are actually 4 different ways you could win: you could hold the button for 2, 3, 4, or 5 milliseconds at the start of the race. In the second race, you could hold the button for at least 4 milliseconds and at most 11 milliseconds and beat the record, a total of 8 different ways to win. In the third race, you could hold the button for at least 11 milliseconds and no more than 19 milliseconds and still beat the record, a total of 9 ways you could win. To see how much margin of error you have, determine the number of ways you can beat the record in each race; in this example, if you multiply these values together, you get 288 (4 * 8 * 9). Determine the number of ways you could beat the record in each race. What do you get if you multiply these numbers together?	97
--- Day 14: Reindeer Olympics --- This year is the Reindeer Olympics! Reindeer can fly at high speeds, but must rest occasionally to recover their energy. Santa would like to know which of his reindeer is fastest, and so he has them race. Reindeer can only either be flying (always at their top speed) or resting (not moving at all), and always spend whole seconds in either state. For example, suppose you have the following Reindeer: Comet can fly 14 km/s for 10 seconds, but then must rest for 127 seconds. Dancer can fly 16 km/s for 11 seconds, but then must rest for 162 seconds. After one second, Comet has gone 14 km, while Dancer has gone 16 km. After ten seconds, Comet has gone 140 km, while Dancer has gone 160 km. On the eleventh second, Comet begins resting (staying at 140 km), and Dancer continues on for a total distance of 176 km. On the 12th second, both reindeer are resting. They continue to rest until the 138th second, when Comet flies for another ten seconds. On the 174th second, Dancer flies for another 11 seconds. In this example, after the 1000th second, both reindeer are resting, and Comet is in the lead at 1120 km (poor Dancer has only gotten 1056 km by that point). So, in this situation, Comet would win (if the race ended at 1000 seconds). Given the descriptions of each reindeer (in your puzzle input), after exactly 2503 seconds, what distance has the winning reindeer traveled?	98
--- Day 14: Disk Defragmentation --- Suddenly, a scheduled job activates the system's disk defragmenter. Were the situation different, you might sit and watch it for a while, but today, you just don't have that kind of time. It's soaking up valuable system resources that are needed elsewhere, and so the only option is to help it finish its task as soon as possible. The disk in question consists of a 128x128 grid; each square of the grid is either free or used. On this disk, the state of the grid is tracked by the bits in a sequence of knot hashes. A total of 128 knot hashes are calculated, each corresponding to a single row in the grid; each hash contains 128 bits which correspond to individual grid squares. Each bit of a hash indicates whether that square is free (0) or used (1). The hash inputs are a key string (your puzzle input), a dash, and a number from 0 to 127 corresponding to the row. For example, if your key string were flqrgnkx, then the first row would be given by the bits of the knot hash of flqrgnkx-0, the second row from the bits of the knot hash of flqrgnkx-1, and so on until the last row, flqrgnkx-127. The output of a knot hash is traditionally represented by 32 hexadecimal digits; each of these digits correspond to 4 bits, for a total of 4 * 32 = 128 bits. To convert to bits, turn each hexadecimal digit to its equivalent binary value, high-bit first: 0 becomes 0000, 1 becomes 0001, e becomes 1110, f becomes 1111, and so on; a hash that begins with a0c2017... in hexadecimal would begin with 10100000110000100000000101110000... in binary. Continuing this process, the first 8 rows and columns for key flqrgnkx appear as follows, using # to denote used squares, and . to denote free ones: ##.#.#..--> .#.#.#.# ....#.#. #.#.##.# .##.#... ##..#..# .#...#.. ##.#.##.--> \| \| V V In this example, 8108 squares are used across the entire 128x128 grid. Given your actual key string, how many squares are used?	99

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