66 lines
1.8 KiB
Elixir
66 lines
1.8 KiB
Elixir
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defmodule Day17Part2 do
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def run do
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File.read!("input")
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|> String.split("\n", trim: true)
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|> parse_input()
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|> boot(6)
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|> Enum.count()
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|> IO.puts()
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end
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def parse_input(input) do
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{_y, cubes} =
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Enum.reduce(input, {0, MapSet.new()}, fn row, {y, cubes} ->
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{_x, cubes} =
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Enum.reduce(String.graphemes(row), {0, cubes}, fn
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".", {x, cubes} -> {x + 1, cubes}
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"#", {x, cubes} -> {x + 1, MapSet.put(cubes, {x, y, 0, 0})}
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end)
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{y + 1, cubes}
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end)
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cubes
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end
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def boot(cubes, 0), do: cubes
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def boot(cubes, count), do: boot(cycle(cubes), count - 1)
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def cycle(cubes) do
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{next_cubes, inactives} =
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Enum.reduce(cubes, {MapSet.new(), MapSet.new()}, fn cube, {next_cubes, inactives} ->
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{active_count, inactives} =
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Enum.reduce(neighbours(cube), {0, inactives}, fn neighbour, {active_count, inactives} ->
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if MapSet.member?(cubes, neighbour) do
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{active_count + 1, inactives}
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else
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{active_count, MapSet.put(inactives, neighbour)}
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end
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end)
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next_cubes = if active_count in 2..3, do: MapSet.put(next_cubes, cube), else: next_cubes
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{next_cubes, inactives}
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end)
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Enum.reduce(inactives, next_cubes, fn inactive, next_cubes ->
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active_neighbours =
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inactive |> neighbours() |> MapSet.new() |> MapSet.intersection(cubes) |> Enum.count()
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if active_neighbours == 3, do: MapSet.put(next_cubes, inactive), else: next_cubes
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end)
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end
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def neighbours({x, y, z, w} = me) do
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all =
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for x <- (x - 1)..(x + 1),
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y <- (y - 1)..(y + 1),
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z <- (z - 1)..(z + 1),
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w <- (w - 1)..(w + 1),
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do: {x, y, z, w}
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all -- [me]
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end
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end
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Day17Part2.run()
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