def lcs[T]: (List[T], List[T]) => List[T] = {
    case (_, Nil) => Nil
    case (Nil, _) => Nil
    case (x :: xs, y :: ys) if x == y => x :: lcs(xs, ys)
    case (x :: xs, y :: ys)           => {
      (lcs(x :: xs, ys), lcs(xs, y :: ys)) match {
        case (xs, ys) if xs.length > ys.length => xs
        case (xs, ys)                          => ys
      }
    }
  }