day24.ex

defmodule Day24 do

  def strength(bridge) do
    bridge
    |> Enum.reduce(0, fn { p1, p2 }, acc -> acc + p1 + p2 end)
  end

  def find_max_bridge(start, []) do
    { start, strength(start) }
  end

  def find_max_bridge(start, free_blocks) do
    next_port = Enum.at(start, 0) |> elem(0)

    free_blocks
    |> Enum.map(fn
      { pr, pl } when pl == next_port ->
        find_max_bridge([ { pr, pl } | start], List.delete(free_blocks, { pr, pl }));

      { pr, pl } when pr == next_port ->
        find_max_bridge([ { pl, pr } | start], List.delete(free_blocks, { pr, pl }));

      _ -> find_max_bridge(start, [])
    end)
    |> Enum.sort_by(
      fn x -> x end,
      fn
        { b1, _ }, { b2, _ }   when length(b1) > length(b2)  -> true;
        { b1, s1 }, { b2, s2 } when length(b1) == length(b2) -> s1 > s2;
        _, _ -> false
      end
    )
    |> Enum.at(0)
  end
end

free_blocks = IO.stream(:stdio, :line)
              |> Stream.map(&String.trim/1)
              |> Enum.map(&String.split(&1, "/"))
              |> Enum.map(fn x -> x |> Enum.map(&String.to_integer/1) end)
              |> Enum.map(&List.to_tuple/1)

Day24.find_max_bridge([{ 0, 0 }], free_blocks)
|> IO.inspect