defmodule Fish do
  def fish(a, b) do
    size = length(a)

    {_stack, dead} =
      a
      |> Enum.zip(b)
      |> Enum.reduce({[], 0}, fn {size_i, dir_i}, {stack, dead} ->
        if dir_i == 1 do
          {[size_i | stack], dead}
        else
          fight(size_i, stack, dead)
        end
      end)

    size - dead
  end

  defp fight(_size_i, [], dead), do: {[], dead}

  defp fight(size_i, [top | rest] = stack, dead) do
    if size_i > top do
      fight(size_i, rest, dead + 1)
    else
      {stack, dead + 1}
    end
  end
end