17-225401.scala

// def rpnPrime(str: String): String = str match {
//   case str if str(4) == '+' => (str(0).asDigit + str(2).asDigit).toString
//   case str if str(4) == '-' => (str(0).asDigit - str(2).asDigit).toString
//   case str if str(4) == '*' => (str(0).asDigit * str(2).asDigit).toString
//   case str if str(4) == '/' => (str(0).asDigit / str(2).asDigit).toString
//   case str if str(4) == '%' => (str(0).asDigit % str(2).asDigit).toString
//   case _ => {
//     ""
//   }
// }

// println(rpnPrime("1 3 +"))
// println(rpnPrime("1 3 h"))

def rpn(str: String): List[String] = {
  val xs = str.split(" ").toList
  xs.foldLeft(List()){ xs => rpnPrime(xs.take(3)) }
  // case xs if xs.length == 3 => rpnPrime(xs)
  // case xs => {
  //   println(xs)
  //   rpnPrime((rpnPrime(xs.take(3)) + " " + rpn(xs.drop(3).mkString(" "))).split(" ").toList)
  // }
}

def rpnPrime(str: List[String]): List[String] = str match {
  case x::y::z if z.head == "+" => (y.toInt + x.toInt).toString
  case x::y::z if z.head == "-" => (y.toInt - x.toInt).toString
  case x::y::z if z.head == "*" => (y.toInt * x.toInt).toString
  case x::y::z if z.head == "/" => (y.toInt / x.toInt).toString
  case x::y::z if z.head == "%" => (y.toInt % x.toInt).toString
  case _ => {
    ""
  }
}


println(rpn("1 3 +"))
println(rpn("1 3 + 5 2 - *"))