1. 题目

2. 思路

(1) 栈

• 利用栈求解后缀表达式即可。

3. 代码

import java.util.Deque;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Set;public class Test {public static void main(String[] args) {}
}class Solution {public int evalRPN(String[] tokens) {Set<String> set = new HashSet<String>() {{add("+");add("-");add("*");add("/");}};Deque<Integer> stack = new LinkedList<>();for (int i = 0; i < tokens.length; i++) {String str = tokens[i];if (set.contains(str)) {int num2 = stack.pop();int num1 = stack.pop();stack.push(calculate(num1, num2, str));} else {stack.push(Integer.parseInt(str));}}return stack.pop();}private int calculate(int num1, int num2, String operation) {int res = 0;switch (operation) {case "+":res = num1 + num2;break;case "-":res = num1 - num2;break;case "*":res = num1 * num2;break;case "/":res = num1 / num2;break;}return res;}
}