def trees_in_trajectory(levels, across), do: trees_in_trajectory(levels, across, 1)

  def trees_in_trajectory(levels, across) do

  def trees_in_trajectory(levels, across, down) do

    |> Enum.take_every(down)

    |> Enum.map(fn {level, level_n} -> get_cell_in_level(level, level_n * across) end)

    |> Enum.map(fn {level, level_n} ->
      get_cell_in_level(level, level_n * across)
    end)

    2 = TobogganTrajectory.trees_in_trajectory("###\n###\n###", 1, 2)