147 lines
5.8 KiB
Plaintext
147 lines
5.8 KiB
Plaintext
Advent of Code
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--- Day 9: Disk Fragmenter ---
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Another push of the button leaves you in the familiar hallways of some
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friendly [16]amphipods! Good thing you each somehow got your own personal
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mini submarine. The Historians jet away in search of the Chief, mostly by
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driving directly into walls.
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While The Historians quickly figure out how to pilot these things, you
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notice an amphipod in the corner struggling with his computer. He's trying
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to make more contiguous free space by compacting all of the files, but his
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program isn't working; you offer to help.
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He shows you the disk map (your puzzle input) he's already generated. For
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example:
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2333133121414131402
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The disk map uses a dense format to represent the layout of files and free
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space on the disk. The digits alternate between indicating the length of a
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file and the length of free space.
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So, a disk map like 12345 would represent a one-block file, two blocks of
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free space, a three-block file, four blocks of free space, and then a
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five-block file. A disk map like 90909 would represent three nine-block
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files in a row (with no free space between them).
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Each file on disk also has an ID number based on the order of the files as
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they appear before they are rearranged, starting with ID 0. So, the disk
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map 12345 has three files: a one-block file with ID 0, a three-block file
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with ID 1, and a five-block file with ID 2. Using one character for each
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block where digits are the file ID and . is free space, the disk map 12345
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represents these individual blocks:
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0..111....22222
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The first example above, 2333133121414131402, represents these individual
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blocks:
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00...111...2...333.44.5555.6666.777.888899
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The amphipod would like to move file blocks one at a time from the end of
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the disk to the leftmost free space block (until there are no gaps
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remaining between file blocks). For the disk map 12345, the process looks
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like this:
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0..111....22222
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02.111....2222.
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022111....222..
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0221112...22...
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02211122..2....
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022111222......
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The first example requires a few more steps:
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00...111...2...333.44.5555.6666.777.888899
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009..111...2...333.44.5555.6666.777.88889.
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0099.111...2...333.44.5555.6666.777.8888..
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00998111...2...333.44.5555.6666.777.888...
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009981118..2...333.44.5555.6666.777.88....
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0099811188.2...333.44.5555.6666.777.8.....
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009981118882...333.44.5555.6666.777.......
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0099811188827..333.44.5555.6666.77........
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00998111888277.333.44.5555.6666.7.........
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009981118882777333.44.5555.6666...........
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009981118882777333644.5555.666............
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00998111888277733364465555.66.............
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0099811188827773336446555566..............
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The final step of this file-compacting process is to update the filesystem
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checksum. To calculate the checksum, add up the result of multiplying each
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of these blocks' position with the file ID number it contains. The
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leftmost block is in position 0. If a block contains free space, skip it
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instead.
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Continuing the first example, the first few blocks' position multiplied by
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its file ID number are 0 * 0 = 0, 1 * 0 = 0, 2 * 9 = 18, 3 * 9 = 27, 4 * 8
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= 32, and so on. In this example, the checksum is the sum of these, 1928.
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Compact the amphipod's hard drive using the process he requested. What is
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the resulting filesystem checksum? (Be careful copy/pasting the input for
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this puzzle; it is a single, very long line.)
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Your puzzle answer was 6211348208140.
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--- Part Two ---
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Upon completion, two things immediately become clear. First, the disk
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definitely has a lot more contiguous free space, just like the amphipod
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hoped. Second, the computer is running much more slowly! Maybe introducing
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all of that [17]file system fragmentation was a bad idea?
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The eager amphipod already has a new plan: rather than move individual
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blocks, he'd like to try compacting the files on his disk by moving whole
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files instead.
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This time, attempt to move whole files to the leftmost span of free space
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blocks that could fit the file. Attempt to move each file exactly once in
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order of decreasing file ID number starting with the file with the highest
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file ID number. If there is no span of free space to the left of a file
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that is large enough to fit the file, the file does not move.
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The first example from above now proceeds differently:
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00...111...2...333.44.5555.6666.777.888899
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0099.111...2...333.44.5555.6666.777.8888..
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0099.1117772...333.44.5555.6666.....8888..
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0099.111777244.333....5555.6666.....8888..
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00992111777.44.333....5555.6666.....8888..
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The process of updating the filesystem checksum is the same; now, this
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example's checksum would be 2858.
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Start over, now compacting the amphipod's hard drive using this new method
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instead. What is the resulting filesystem checksum?
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Your puzzle answer was 6239783302560.
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Both parts of this puzzle are complete! They provide two gold stars: **
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At this point, you should [18]return to your Advent calendar and try
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another puzzle.
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If you still want to see it, you can [19]get your puzzle input.
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References
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Visible links
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1. https://adventofcode.com/
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2. https://adventofcode.com/2024/about
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3. https://adventofcode.com/2024/events
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4. https://cottonbureau.com/people/advent-of-code
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5. https://adventofcode.com/2024/settings
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6. https://adventofcode.com/2024/auth/logout
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7. Advent of Code Supporter
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https://adventofcode.com/2024/support
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8. https://adventofcode.com/2024
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9. https://adventofcode.com/2024
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10. https://adventofcode.com/2024/support
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12. https://adventofcode.com/2024/leaderboard
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13. https://adventofcode.com/2024/stats
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16. https://adventofcode.com/2021/day/23
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17. https://en.wikipedia.org/wiki/File_system_fragmentation
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18. https://adventofcode.com/2024
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19. https://adventofcode.com/2024/day/9/input
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