cost_test.ex

ExUnit.start()
ExUnit.configure(exclude: :pending, trace: true)

defmodule CostTest do
  use ExUnit.Case

  def cost([]), do: 0
  def cost([_last]), do: 0
  def cost([current | [next | tail]]) do
    Enum.min([current + cost([next | tail]), next + cost(tail)])
  end

  test "1" do
    assert cost([10, 15, 20]) == 15
  end

  test "2" do
    assert cost([1, 100, 1, 1, 1, 100, 1, 1, 100, 1]) == 6
  end
end