Day 14: Regolith Reservoir

text = File.read!("Code/aoc.ex/input/2022/14.txt")

Regolith Reservoir

example = """
498,4 -> 498,6 -> 496,6
503,4 -> 502,4 -> 502,9 -> 494,9
"""

structure =
  for line <- String.split(text, "\n", trim: true) do
    points =
      for p <- String.split(line, " -> ") do
        for c <- String.split(p, ","), do: String.to_integer(c)
      end

    segments =
      points
      |> Enum.chunk_every(2, 1, :discard)
      |> Enum.map(fn
        [[x, py], [x, qy]] -> Enum.map(py..qy, &amp;{x, &amp;1})
        [[px, y], [qx, y]] -> Enum.map(px..qx, &amp;{&amp;1, y})
        [[px, py], [qx, _]] -> Enum.map(px..py, &amp;{&amp;1, &amp;1 - px + qx})
      end)

    segments
  end
  |> List.flatten()
  |> MapSet.new()

structure_size = MapSet.size(structure)

bottom = structure |> Enum.map(&amp;elem(&amp;1, 1)) |> Enum.max()

Part One

Stream.iterate({{500, 0}, structure}, fn {{x, y}, structure} ->
  cond do
    not MapSet.member?(structure, {x, y + 1}) -> {{x, y + 1}, structure}
    not MapSet.member?(structure, {x - 1, y + 1}) -> {{x - 1, y + 1}, structure}
    not MapSet.member?(structure, {x + 1, y + 1}) -> {{x + 1, y + 1}, structure}
    true -> {{500, 0}, MapSet.put(structure, {x, y})}
  end
end)
|> Enum.find(fn {{_, y}, _} -> y > bottom end)
|> elem(1)
|> MapSet.size()
|> Kernel.-(structure_size)

Part Two

Stream.iterate({{500, 0}, structure}, fn {{x, y}, structure} ->
  cond do
    y == bottom + 1 -> {{500, 0}, MapSet.put(structure, {x, y})}
    not MapSet.member?(structure, {x, y + 1}) -> {{x, y + 1}, structure}
    not MapSet.member?(structure, {x - 1, y + 1}) -> {{x - 1, y + 1}, structure}
    not MapSet.member?(structure, {x + 1, y + 1}) -> {{x + 1, y + 1}, structure}
    true -> {{500, 0}, MapSet.put(structure, {x, y})}
  end
end)
|> Enum.find(fn {_, sand} -> MapSet.member?(sand, {500, 0}) end)
|> elem(1)
|> MapSet.size()
|> Kernel.-(structure_size)