릿코드 150. Evaluate Reverse Polish Notation 코틀린

뭐 이상한 계산법을 써서 계산하라는문제
숫자를 만나면 숫자를 스택에 넣고,연산기호를 만나면 스택에서 2개뺴서 연산을 한다음 스택에 다시 넣음


정답

import java.util.Stack

class Solution {
    fun evalRPN(tokens: Array<String>): Int {
        val stack = Stack<Int>()

        for (i in tokens){
            if (i.toIntOrNull()!=null){
                stack.push(i.toInt())
            }else{
                val first=stack.pop()
                val second=stack.pop()
                when(i){
                    "+"->{stack.push(second+first)}
                    "-"->{stack.push(second-first)}
                    "*"->{stack.push(second*first)}
                    "/"->{stack.push(second/first)}
                }
            }
        }

        println(stack.peek())
        return stack.pop()
    }
}