一、题目内容

二、题解

解法1：

思路

使用栈，遇见数字入栈，遇见符号，弹出两个数字做运算，然后将结果入栈

代码

class Solution {
    public int evalRPN(String[] tokens) {
        Stack<Integer> stack = new Stack<Integer>();
        for(String token: tokens){
            if(isNumber(token)){
                stack.push(Integer.parseInt(token));
            }else{
                Integer num1 = stack.pop();
                Integer num2 = stack.pop();
                switch (token) {
                    case "+":
                        stack.push(num1 + num2);
                        break;
                    case "-":
                        stack.push(num1 - num2);
                        break;
                    case "*":
                        stack.push(num1 * num2);
                        break;
                    case "/":
                        stack.push(num1 / num2);
                        break;
                    default:
                }
            }
        }
        return stack.pop();
    }
    public boolean isNumber(String token) {
        return !("+".equals(token) || "-".equals(token) || "*".equals(token) || "/".equals(token));
    }
}