题解 | #逆波兰表达式求值#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param tokens string字符串一维数组
     * @return int整型
     */
    public int evalRPN(String[] tokens) {
        // write code here
        int res = 0; // 定义一个整型变量，用于存放最终的返回结果
        int num1 = 0;
        int num2 = 0;
        Stack<Integer> stack = new Stack<>();
        for (int i = 0; i < tokens.length; i++) {
            String token = tokens[i];
            switch (token) {
                case "+":
                    num1 = stack.pop();
                    num2 = stack.pop();
                    res = num2 + num1;
                    stack.push(res);
                    break;
                case "-":
                    num1 = stack.pop();
                    num2 = stack.pop();
                    res = num2 - num1;
                    stack.push(res);
                    break;
                case "*":
                    num1 = stack.pop();
                    num2 = stack.pop();
                    res = num2 * num1;
                    stack.push(res);
                    break;
                case "/":
                    num1 = stack.pop();
                    num2 = stack.pop();
                    res = num2 / num1;
                    stack.push(res);
                    break;
                default:
                    stack.push(Integer.valueOf(token));
            }
        }
        res = stack.pop();
        return res;
    }
}