102 lines
3 KiB
Elixir
102 lines
3 KiB
Elixir
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defmodule Day12 do
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defmodule Parser do
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def parse(filename) when is_binary(filename) do
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File.open!(filename, [:utf8], &parse/1)
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end
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def parse(file) do
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IO.read(file, String.length("initial state: "))
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state = file |> IO.read(:line) |> String.trim() |> String.to_charlist() |> Enum.with_index()
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IO.read(file, :line)
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{state, parse_spec(file)}
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end
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def parse_spec(file), do: parse_spec(file, IO.read(file, :line), %{})
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def parse_spec(_file, :eof, spec), do: spec
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def parse_spec(file, line, spec) do
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[pattern, <<result::utf8>>] = ~r/(.{5}) => (.)/ |> Regex.run(line, capture: :all_but_first)
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parse_spec(
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file,
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IO.read(file, :line),
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Map.put(spec, String.to_charlist(pattern), result)
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)
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end
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end
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def evolve(input, _spec, 0, _previous), do: input
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def evolve(input, spec, generations, previous) do
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next = generation(input, spec)
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IO.inspect("#{generations}: #{next |> visualise}")
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if stable?(next, input) do
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# Stable state, so we can just add the remaining generation count to the index numbers and finish early
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next = Enum.map(next, fn {pot, idx} -> {pot, idx + generations - 1} end)
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evolve(next, spec, 0, input)
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else
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evolve(next, spec, generations - 1, input)
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end
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end
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def stable?(next, prev), do: visualise(next) === visualise(prev)
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def generation(input, spec) do
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input |> pad |> propagate(spec) |> strip
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end
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def propagate([a, b, c, d, e | rest], spec) do
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{_, pot} = c
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pattern = visualise([a, b, c, d, e])
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[{Map.get(spec, pattern), pot} | propagate([b, c, d, e | rest], spec)]
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end
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def propagate(rest, _spec) when length(rest) == 4, do: []
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# Pads with 4 empty pots. If the spec contained ..... => #, would need to pad with 5
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def pad(list) do
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list |> Enum.reverse() |> pad_rear |> Enum.reverse() |> pad_front
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end
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def pad_front([{?., _}, {?., _}, {?., _}, {?., _} | _] = done), do: done
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def pad_front([{_, i} | _] = list), do: pad_front([{?., i - 1} | list])
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def pad_rear([{?., _}, {?., _}, {?., _}, {?., _} | _] = done), do: done
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def pad_rear([{_, i} | _] = list), do: pad_rear([{?., i + 1} | list])
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# Removes leading and trailing empty pots
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def strip([{?., _}]), do: []
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def strip([{?., _} | list]), do: strip(list)
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def strip([{?#, _} | _] = list), do: strip_tl(Enum.reverse(list))
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def strip_tl([{?., _} | list]), do: strip_tl(list)
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def strip_tl(list), do: Enum.reverse(list)
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def visualise(input) do
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Enum.map(input, fn {x, _i} -> x end)
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end
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def part1 do
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{input, spec} = Parser.parse("input")
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evolve(input, spec, 20, [])
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|> Enum.filter(fn {plant, _} -> plant === ?# end)
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|> Enum.map(fn {_, pot} -> pot end)
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|> Enum.sum()
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end
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def part2 do
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{input, spec} = Parser.parse("input")
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evolve(input, spec, 50_000_000_000, [])
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|> Enum.filter(fn {plant, _} -> plant === ?# end)
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|> Enum.map(fn {_, pot} -> pot end)
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|> Enum.sum()
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end
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end
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part1 = Day12.part1()
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part2 = Day12.part2()
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IO.puts("part 1: #{part1}")
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IO.puts("part 2: #{part2}")
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