leetcode-20-Valid Parentheses

                                    Valid Parentheses 

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.

括号匹配，使用栈求解。

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