LeetCode/com/zerroi/leetcode/Three22/EvalRPN.java

package com.zerroi.leetcode.Three22;

import java.util.Deque;
import java.util.LinkedList;
import java.util.Stack;

public class EvalRPN {
    public static void main(String[] args) {
        SolutionFirst solutionFirst = new SolutionFirst();
//        int res = solutionFirst.evalRPN(new String[]{"2", "1", "+", "3", "*"});
        int res = solutionFirst.evalRPN(new String[]{"10","6","9","3","+","-11","*","/","*","17","+","5","+"});
        System.out.println("res = " + res);
    }
}

class SolutionFirst {
    public int evalRPN(String[] tokens) {
        Stack<Integer> stack = new Stack<>();
        int n1 = 0, n2 = 0;
        for (String token : tokens) {
            switch (token) {
                case "+":
                    n1 = stack.pop();
                    n2 = stack.pop();
                    stack.add(n1 + n2);
                    break;
                case "-":
                    n1 = stack.pop();
                    n2 = stack.pop();
                    stack.add(n2 - n1);
                    break;
                case "*":
                    n1 = stack.pop();
                    n2 = stack.pop();
                    stack.add(n1*n2);
                    break;
                case "/":
                    n1 = stack.pop();
                    n2 = stack.pop();
                    stack.add(n2 / n1);
                    break;
                default:
                    stack.add(Integer.valueOf(token));
                    break;
            }
        }
        return stack.isEmpty() ? 0 : stack.getFirst();
    }
}