solving_reverse_polish_ notion.scala

def solveRPN(expression: String):String = {
  expression.split(" ").foldLeft(List[String]()) {
    (stack:List[String], e:String) =>
      e match {
        case "*" =>
          stack match {
            case List(z) => List(z)
              case x :: y :: ys =>  (y.toInt * x.toInt).toString :: ys
          }
        case "+" =>
          stack match {
            case List(z) => List(z)
              case x :: y :: ys =>  (y.toInt + x.toInt).toString :: ys
          }
        case "-"  =>
          stack match {
            case List(z) => List(z)
              case x :: y :: ys =>  (y.toInt - x.toInt).toString :: ys
          }
          case x => x :: stack
      }
  }.head
}