gumimaze https://gist.github.com/cooldaemon/35acccd20d226ee33b639b17156242dc

mission2.diff

9a10
>     Agent.start_link(fn -> 0 end, name: Result)
11,15c12,13
<     try do
<       walk(maze, x, y, %{}, 0)
<     catch
<       pt -> pt
<     end
---
>     walk(maze, x, y, %{}, 0)
>     Agent.get(Result, &(&1))
26c24
<         {_, ?G} -> throw(pt)
---
>         {_, ?G} -> Agent.update(Result, &(Enum.max([&1, pt])))

mission2.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 solve(maze) do
    Agent.start_link(fn -> 0 end, name: Result)
    {x, y} = elem(Enum.find(maze, fn {_, v} -> v == ?S end), 0)
    walk(maze, x, y, %{}, 0)
    Agent.get(Result, &(&1))
  end

  defp walk(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} -> walk(maze, x2, y2, walked, pt)
        {_, ?1} -> walk(maze, x2, y2, walked, pt + 1)
        {_, ?G} -> Agent.update(Result, &(Enum.max([&1, pt])))
      end
    end
  end
end

Gumimaze.read() |> Gumimaze.solve() |> IO.puts() # => 6

mission3.diff

9a10
>     Agent.start_link(fn -> 0 end, name: Result)
11,15c12,13
<     try do
<       walk(maze, x, y, %{}, 0)
<     catch
<       pt -> pt
<     end
---
>     walk(maze, x, y, %{}, 0)
>     Agent.get(Result, &(&1))
24,26c22,24
<         {_, ?\s} -> walk(maze, x2, y2, walked, pt)
<         {_, ?1} -> walk(maze, x2, y2, walked, pt + 1)
<         {_, ?G} -> throw(pt)
---
>         {_, ?\s} -> Task.async(fn -> walk(maze, x2, y2, walked, pt) end) |> Task.await
>         {_, ?1} -> Task.async(fn -> walk(maze, x2, y2, walked, pt + 1) end) |> Task.await
>         {_, ?G} -> Agent.update(Result, &(Enum.max([&1, pt])))

mission3.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 solve(maze) do
    Agent.start_link(fn -> 0 end, name: Result)
    {x, y} = elem(Enum.find(maze, fn {_, v} -> v == ?S end), 0)
    walk(maze, x, y, %{}, 0)
    Agent.get(Result, &(&1))
  end

  defp walk(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} -> Task.async(fn -> walk(maze, x2, y2, walked, pt) end) |> Task.await
        {_, ?1} -> Task.async(fn -> walk(maze, x2, y2, walked, pt + 1) end) |> Task.await
        {_, ?G} -> Agent.update(Result, &(Enum.max([&1, pt])))
      end
    end
  end
end

Gumimaze.read() |> Gumimaze.solve() |> IO.puts()