Day 10: Hoof It

Mix.install([:kino])

Section

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

map =
  input
  |> Kino.Input.read()
  |> String.split()
  |> Enum.with_index()
  |> Enum.reduce(%{}, fn {row, y}, map ->
    row
    |> String.graphemes()
    |> Enum.map(&String.to_integer/1)
    |> Enum.with_index()
    |> Enum.reduce(map, fn {col, x}, map ->
      Map.put(map, {x, y}, col)
    end)
  end)

defmodule TopgraphicMap do
  def trails(map) do
    map
    |> Map.filter(fn {_trail_head, height} -> height == 0 end)
    |> Enum.map(&trails(&1, map))
  end

  defp trails({{x, y}, 9}, _map), do: [{x, y}]

  defp trails({{x, y}, height}, map) do
    map
    |> Map.take([{x + 1, y}, {x - 1, y}, {x, y + 1}, {x, y - 1}])
    |> Map.filter(&(elem(&1, 1) == height + 1))
    |> Enum.flat_map(&trails(&1, map))
  end
end

trails = TopgraphicMap.trails(map)

trails
|> Enum.map(&MapSet.new/1)
|> Enum.map(&MapSet.size/1)
|> Enum.sum()

trails
|> Enum.map(&Enum.count/1)
|> Enum.sum()