LeetCode算法题——20. 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.

采用栈机制，对于每个进栈元素都与栈顶元素进行匹配，若匹配成功，这栈顶元素弹出，若匹配不成功，则进栈

Pyhon实现：

# -*- coding:utf-8 -*-class Solution(object):    def isValid(self, s):        """        :type s: str        :rtype: bool        """        brackets=[]        for i in range(0,s.__len__()):            pipei=False            if len(brackets)!=0:                b=brackets.pop()                if b=='(':                    if s[i]==')':                        pipei=True                elif b=='{':                    if s[i]=='}':                        pipei=True                elif b=='[':                    if s[i]==']':                        pipei=True                if pipei==False:                    brackets.append(b)                    brackets.append(s[i]);            else:                brackets.append(s[i])        if len(brackets)==0:            return True        else:            return False    if __name__=="__main__":    s=Solution()    res=s.isValid("{[)(]}")    print(res)