def r[A](l: List[A]): List[A] = {
    def _reverse(res: List[A], rem: List[A]): List[A] = rem match {
        case Nil => res
        case h :: tail => _reverse(h :: res, tail)
    }
    _reverse(Nil, l)
}

def sumuj (list1:List[Int],list2:List[Int]):List[Int]= {
  def sumuj_2(l1:List[Int],l2:List[Int],temp:List[Int]):List[Int]=
    (l1, l2) match {
  case (Nil,Nil) => r(temp)
  case (Nil,_) => sumuj_2(l1, l2.tail, l2.head::temp)
  case (_,Nil) => sumuj_2(l1.tail, l2, l1.head::temp)
  case (_,_) => sumuj_2(l1.tail, l2.tail, (l1.head + l2.head)::temp)
  }
    sumuj_2(list1,list2,Nil)
}

sumuj (List(1,2,3),List(4,5,6,7,8))
sumuj (List(),List(4,5,6,7,8))