47 lines
No EOL
2.9 KiB
Text
47 lines
No EOL
2.9 KiB
Text
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.
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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*.
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The tiles are all *hexagonal*; they need to be arranged in a [hex grid](https://en.wikipedia.org/wiki/Hexagonal_tiling) with a very specific color pattern. Not in the mood to wait, you offer to help figure out the pattern.
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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.
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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.)
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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.
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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.
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Here is a larger example:
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```
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sesenwnenenewseeswwswswwnenewsewsw
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neeenesenwnwwswnenewnwwsewnenwseswesw
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seswneswswsenwwnwse
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nwnwneseeswswnenewneswwnewseswneseene
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swweswneswnenwsewnwneneseenw
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eesenwseswswnenwswnwnwsewwnwsene
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sewnenenenesenwsewnenwwwse
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wenwwweseeeweswwwnwwe
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wsweesenenewnwwnwsenewsenwwsesesenwne
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neeswseenwwswnwswswnw
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nenwswwsewswnenenewsenwsenwnesesenew
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enewnwewneswsewnwswenweswnenwsenwsw
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sweneswneswneneenwnewenewwneswswnese
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swwesenesewenwneswnwwneseswwne
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enesenwswwswneneswsenwnewswseenwsese
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wnwnesenesenenwwnenwsewesewsesesew
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nenewswnwewswnenesenwnesewesw
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eneswnwswnwsenenwnwnwwseeswneewsenese
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neswnwewnwnwseenwseesewsenwsweewe
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wseweeenwnesenwwwswnew
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```
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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*.
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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?*
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To begin, [get your puzzle input](24/input).
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Answer: |