leetcode Valid Parentheses

题目

Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[’ and ‘]’, determine if the input string is valid.

The brackets must close in the correct order, “()” and “()[]{}” are all valid but “(]” and “([)]” are not.
题目来源：https://leetcode.com/problems/valid-parentheses/

分析

借助一个栈，如果遇到的是左括号，则进栈；如果遇到的是右括号，则与栈顶元素比较。与栈顶元素不match，则return false。扫描完字符串后，栈应该为空。

代码

class Solution {private:    stack<char> my_stack;public:    bool isMatch(char a, char b){//a和b是否是一对括号        if(a == '(' && b == ')')            return true;        else if(a == '[' && b == ']')            return true;        else if(a == '{' && b == '}')            return true;        else            return false;    }    bool isValid(string s) {        int len = s.length();        if(len <= 0)            return true;        for(int i = 0; i < len ; i++){            char ch = s.at(i);            if(ch == '(' || ch == '{' || ch == '[')//左括号入栈                this->my_stack.push(ch);            else{//右括号与栈顶元素匹配                if(this->my_stack.empty())                    return false;                if(!isMatch(this->my_stack.top(), ch))                    return false;                else                    this->my_stack.pop();            }        }        return my_stack.empty();//扫描结束后栈应该为空，非空则返回false    }};