Erlang & Elixir Fest 2018 gumi quiz mission 2

gumimaze_mission_2.exs

defmodule Gumimaze do
  def read() do
    lines = "maze.txt" |> File.read!() |> String.trim() |> String.split("\n")
    for {line, y} <- Enum.with_index(lines), {c, x} <- Enum.with_index(String.to_charlist(line)), into: %{} do
      {{x, y}, c}
    end
  end
    

  def solve2(maze) do
    {x, y} = elem(Enum.find(maze, fn {_, v} -> v == ?S end), 0)
    
    walk2(maze, x, y, %{}, 0)
    |> List.flatten 
    |> Enum.filter(fn a -> !is_atom(a) end) 
    |> Enum.max 
  end

  defp walk2(maze, x, y, walked, pt) do
    walked = Map.put(walked, {x, y}, true)
    for {x2, y2} <- [{x + 1, y}, {x, y + 1}, {x - 1, y}, {x, y - 1}] do
      case {walked[{x2, y2}], maze[{x2, y2}]} do
        {true, _} -> :walked
        {_, ?W} -> :wall
        {_, ?\s} -> walk2(maze, x2, y2, walked, pt)
        {_, ?1} -> walk2(maze, x2, y2, walked, pt + 1)
        {_, ?G} -> pt
      end
    end
  end


  def main() do
    Gumimaze.read() |> Gumimaze.solve2() |> IO.puts 
  end
end