LeetCode题解(20)--Valid Parentheses

https://leetcode.com/problems/valid-parentheses/

原题：

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.

思路:

考察stack的应用。

我的AC代码:

class Solution {
public:
    bool isValid(string s) {
        int n=s.size();
        if(n%2==1)
            return false;
        stack<char> a;    //push,pop,top,size
         for(int i=0;i<n;i++){
            if(s[i]=='('|| s[i]=='['||s[i]=='{') 
                a.push(s[i]);
            else if (a.empty()==false &&( (a.top()=='(' && s[i]==')') || (a.top()=='[' && s[i]==']') || (a.top()=='{' && s[i]=='}') ) )
                a.pop();
            else 
                return false;
         }
         if(a.empty())
            return true;
         else return false;
    }
};