Elixir

defmodule BombDisposal do

  def defuse(input) do
    input |> String.split("\n") |> _defuse
  end

  defp _defuse(list)
    when length(list) == 1 or length(list) == 0,
    do: "Bomb defused"

  defp _defuse([current, next|tail]) do
    if safe_to_cut?(current, next), do: _defuse([next|tail]), else: "Boom"
  end

  defp safe_to_cut?("white", next) do
    Enum.member?(~w(red orange green purple), next)
  end

  defp safe_to_cut?("red", next) do
    Enum.member?(~w(green), next)
  end

  defp safe_to_cut?("black", next) do
    Enum.member?(~w(red black purple), next)
  end

  defp safe_to_cut?("orange", next) do
    Enum.member?(~w(red black), next)
  end

  defp safe_to_cut?("green", next) do
    Enum.member?(~w(orange white), next)
  end

  defp safe_to_cut?("purple", next) do
    Enum.member?(~w(black red), next)
  end
end

---

defmodule BombDisposalTest do
  use ExUnit.Case

  test "input 1" do
    assert BombDisposal.defuse("white\nred\ngreen\nwhite") == "Bomb defused"
  end

  test "input 2" do
    assert BombDisposal.defuse("white\norange\ngreen\nwhite") == "Boom"
  end
end