foo.scala

  def p12[T](list: Seq[(Int, T)]): Seq[T] = {
    @tailrec
    def p12inner(listInner: Seq[(Int, T)], acc: List[T]): Seq[T] = {
      if (listInner.isEmpty) acc
      else
        p12inner(listInner.tail, acc ::: List.fill(listInner.head._1)(listInner.head._2))
    }
    p12inner(list, List())
  }