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alexchao26
58 lines
2.1 KiB
Plaintext
58 lines
2.1 KiB
Plaintext
--- Day 24: Planet of Discord ---
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You land on Eris, your last stop before reaching Santa. As soon as you do, your sensors start picking up strange life forms moving around: Eris is infested with bugs! With an over 24-hour roundtrip for messages between you and Earth, you'll have to deal with this problem on your own.
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Eris isn't a very large place; a scan of the entire area fits into a 5x5 grid (your puzzle input). The scan shows bugs (#) and empty spaces (.).
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Each minute, The bugs live and die based on the number of bugs in the four adjacent tiles:
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A bug dies (becoming an empty space) unless there is exactly one bug adjacent to it.
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An empty space becomes infested with a bug if exactly one or two bugs are adjacent to it.
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Otherwise, a bug or empty space remains the same. (Tiles on the edges of the grid have fewer than four adjacent tiles; the missing tiles count as empty space.) This process happens in every location simultaneously; that is, within the same minute, the number of adjacent bugs is counted for every tile first, and then the tiles are updated.
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Here are the first few minutes of an example scenario:
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Initial state:
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....#
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#..#.
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#..##
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..#..
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#....
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After 1 minute:
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#..#.
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####.
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###.#
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##.##
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.##..
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After 2 minutes:
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#####
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....#
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....#
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...#.
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#.###
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After 3 minutes:
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#....
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####.
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...##
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#.##.
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.##.#
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After 4 minutes:
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####.
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....#
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##..#
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.....
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##...
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To understand the nature of the bugs, watch for the first time a layout of bugs and empty spaces matches any previous layout. In the example above, the first layout to appear twice is:
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.....
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.....
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.....
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#....
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.#...
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To calculate the biodiversity rating for this layout, consider each tile left-to-right in the top row, then left-to-right in the second row, and so on. Each of these tiles is worth biodiversity points equal to increasing powers of two: 1, 2, 4, 8, 16, 32, and so on. Add up the biodiversity points for tiles with bugs; in this example, the 16th tile (32768 points) and 22nd tile (2097152 points) have bugs, a total biodiversity rating of 2129920.
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What is the biodiversity rating for the first layout that appears twice?
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