Day 4: Printing Department

Mix.install([:kino])

Section

input = Kino.Input.textarea("input", monospace: true)

input
|> Kino.Input.read()
|> String.split()
|> Enum.with_index()
|> Enum.reduce(MapSet.new(), fn {row, y}, rolls ->
  row
  |> String.graphemes()
  |> Enum.with_index()
  |> Enum.reduce(rolls, fn
    {"@", x}, rolls -> MapSet.put(rolls, {x, y})
    _, rolls -> rolls
  end)
end)
|> then(fn rolls ->
  Enum.count(rolls, fn {x, y} ->
    MapSet.size(
      MapSet.intersection(
        for dx <- (x - 1)..(x + 1),
            dy <- (y - 1)..(y + 1),
            {dx, dy} != {x, y},
            into: MapSet.new() do
          {dx, dy}
        end,
        rolls
      )
    ) < 4
  end)
end)

defmodule Mapper do
  def print(map) do
    IO.puts(
      Enum.map_join(0..elem(Enum.max_by(map, &elem(&1, 1)), 1), fn y ->
        Enum.map_join(0..elem(Enum.max_by(map, &elem(&1, 0)), 0), fn x ->
          if {x, y} in map, do: "@", else: "."
        end) <> "\n"
      end)
    )
  end
end

input
|> Kino.Input.read()
|> String.split()
|> Enum.with_index()
|> Enum.reduce(MapSet.new(), fn {row, y}, rolls ->
  row
  |> String.graphemes()
  |> Enum.with_index()
  |> Enum.reduce(rolls, fn
    {"@", x}, rolls -> MapSet.put(rolls, {x, y})
    _, rolls -> rolls
  end)
end)
|> Stream.iterate(fn rolls ->
  MapSet.reject(rolls, fn {x, y} ->
    MapSet.size(
      MapSet.intersection(
        for dx <- (x - 1)..(x + 1),
            dy <- (y - 1)..(y + 1),
            {dx, dy} != {x, y},
            into: MapSet.new() do
          {dx, dy}
        end,
        rolls
      )
    ) < 4
  end)
end)
|> Stream.chunk_every(2, 1)
|> Enum.reduce_while(0, fn
  [rolls, rolls], count ->
    Mapper.print(rolls)
    {:halt, count}

  [prev, next], count ->
    {:cont, count + MapSet.size(prev) - MapSet.size(next)}
end)