72 lines
1.9 KiB
Elixir
72 lines
1.9 KiB
Elixir
defmodule Aoc2023.Day16 do
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use Aoc2023
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defp emissions(char, dir) do
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case {char, dir} do
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{?., dir} -> [dir]
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{?-, {0, dir}} -> [{0, dir}]
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{?-, {_, 0}} -> [{0, -1}, {0, 1}]
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{?|, {dir, 0}} -> [{dir, 0}]
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{?|, {0, _}} -> [{-1, 0}, {1, 0}]
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{?/, {dir, 0}} -> [{0, -dir}]
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{?/, {0, dir}} -> [{-dir, 0}]
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{?\\, {dir, 0}} -> [{0, dir}]
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{?\\, {0, dir}} -> [{dir, 0}]
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end
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end
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defp add_vec({y, x}, {y_, x_}) do
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{y + y_, x + x_}
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end
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def parse(input) do
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input
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|> lines
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|> Enum.map(&String.to_charlist/1)
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|> Enum.with_index()
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|> Enum.flat_map(fn {row, y} ->
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row |> Enum.with_index() |> Enum.map(fn {c, x} -> {{y, x}, c} end)
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end)
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|> Enum.into(%{})
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end
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defp run(input, heads) do
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loop = fn recur, energized, heads ->
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energized_ = MapSet.union(energized, heads |> MapSet.new())
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heads_ =
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heads
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|> Enum.flat_map(fn {coord, dir} ->
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char = Map.get(input, coord)
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if char,
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do:
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emissions(char, dir)
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|> Enum.map(&{add_vec(coord, &1), &1})
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|> Enum.reject(&MapSet.member?(energized_, &1))
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|> Enum.filter(&Map.has_key?(input, elem(&1, 0))),
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else: []
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end)
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if length(heads_) > 0, do: recur.(recur, energized_, heads_), else: energized_
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end
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loop.(loop, MapSet.new(), heads) |> Enum.map(pipe(elem(0))) |> MapSet.new() |> MapSet.size()
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end
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def part1(input) do
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run(input, [{{0, 0}, {0, 1}}])
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end
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def part2(input) do
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{my, mx} = input |> Enum.map(pipe(elem(0))) |> Enum.max()
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[
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0..my |> Enum.map(&{{&1, 0}, {0, 1}}),
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0..my |> Enum.map(&{{&1, mx}, {0, -1}}),
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0..mx |> Enum.map(&{{0, &1}, {1, 0}}),
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0..mx |> Enum.map(&{{my, &1}, {-1, 0}})
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] |> Enum.concat |> Enum.map(&run(input, [&1])) |> Enum.max
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end
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end
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