53 lines
1.4 KiB
Elixir
53 lines
1.4 KiB
Elixir
defmodule Cell do
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defstruct [:x, :y]
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end
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defmodule Day24Part1 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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|> Enum.map(&parse_line/1)
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|> Enum.map(&to_cell/1)
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|> Enum.reduce(MapSet.new(), fn cell, black ->
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if MapSet.member?(black, cell) do
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MapSet.delete(black, cell)
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else
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MapSet.put(black, cell)
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end
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end)
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|> Enum.count()
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|> IO.puts()
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end
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def parse_line(str) do
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str
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|> String.graphemes()
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|> Enum.chunk_while(
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nil,
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fn
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"n", nil -> {:cont, :north}
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"s", nil -> {:cont, :south}
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"e", :north -> {:cont, :northeast, nil}
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"e", :south -> {:cont, :southeast, nil}
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"e", nil -> {:cont, :east, nil}
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"w", :north -> {:cont, :northwest, nil}
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"w", :south -> {:cont, :southwest, nil}
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"w", nil -> {:cont, :west, nil}
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end,
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fn acc -> {:cont, acc} end
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)
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end
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def to_cell(directions) do
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Enum.reduce(directions, %Cell{x: 0, y: 0}, &move/2)
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end
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def move(:east, %Cell{x: x, y: y}), do: %Cell{x: x + 2, y: y}
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def move(:west, %Cell{x: x, y: y}), do: %Cell{x: x - 2, y: y}
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def move(:northeast, %Cell{x: x, y: y}), do: %Cell{x: x + 1, y: y + 1}
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def move(:northwest, %Cell{x: x, y: y}), do: %Cell{x: x - 1, y: y + 1}
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def move(:southeast, %Cell{x: x, y: y}), do: %Cell{x: x + 1, y: y - 1}
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def move(:southwest, %Cell{x: x, y: y}), do: %Cell{x: x - 1, y: y - 1}
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end
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Day24Part1.run()
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