def divideLists(xs:List[Int]) : (List[Int] , List[Int]) =
{
  if(xs.isEmpty) (Nil,Nil)
  else if(xs.head < 0 ) (xs.head::divideLists(xs.tail)._1,
    if(xs.head % 2 == 0) divideLists(xs.tail)._2 else xs.head::divideLists(xs.tail)._2)
  else divideLists(xs.tail)
}

divideLists(List(-3, -6, 8, -9, 13))