题解 | 逆波兰表达式求值

import java.util.*;

/**
 * NC216 逆波兰表达式求值
 * @author d3y1
 */
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) {
        Stack<Integer> stack = new Stack<>();
        int leftVal,rightVal;
        for(String token: tokens){
            switch(token){
                case "+": rightVal=stack.pop();leftVal=stack.pop();stack.push(leftVal+rightVal); break;
                case "-": rightVal=stack.pop();leftVal=stack.pop();stack.push(leftVal-rightVal); break;
                case "*": rightVal=stack.pop();leftVal=stack.pop();stack.push(leftVal*rightVal); break;
                case "/": rightVal=stack.pop();leftVal=stack.pop();stack.push(leftVal/rightVal); break;
                default: stack.push(Integer.parseInt(token)); break;
            }
        }

        // + - * /
        // String regex = "[+\\-*/]";
        // for(String token: tokens){
        //     if(token.matches(regex)){
        //         rightVal = stack.pop();
        //         leftVal = stack.pop();
        //         switch(token){
        //             case "+": stack.push(leftVal+rightVal); break;
        //             case "-": stack.push(leftVal-rightVal); break;
        //             case "*": stack.push(leftVal*rightVal); break;
        //             case "/": stack.push(leftVal/rightVal); break;
        //             default: break;
        //         }
        //     }else{
        //         stack.push(Integer.parseInt(token));
        //     }
        // }

        return stack.pop();
    }
}