S99_P10.scala

object S99_P10 {
  def encode[T](ts: Seq[T]): Seq[(Int, T)] = {
    val (_, _, l, last) = ts.foldRight[(Int, Option[T], Seq[(Int, T)], (Int, Option[T]))]((0, None, Nil, (0, None))) {
      (el, q) =>
        val (nr, option, acc, _) = q
        option match {
          case None => (1, Some(el), acc, (1, Some(el)))
          case Some(x) => if (x == el) {
            (nr + 1, Some(el), acc, (nr + 1, Some(el)))
          } else {
            (1, Some(el), (nr, x) +: acc, (nr + 1, Some(el)))
          }
        }

    }
    val (nr, opt) = last
    opt match{
      case None =>l
      case Some(x) =>(nr, x) +: l
    }

  }
}