Easy-题目47：20. Valid Parentheses

题目原文：
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.
题目大意：
给出一个括号字符串，判断括号是否正确匹配。
题目分析：
本题考查堆栈的使用，遇到左边的括号全部入栈，遇到右边的括号则看栈顶的括号是不是对应的左括号，如是则弹出，如不是则返回错误。如果整个括号字符串扫完之后栈恰好为空，则是合法匹配。
源码：（language：python）

class Solution(object):    def isValid(self, s):        """        :type s: str        :rtype: bool        """        stack=[]        for c in s:            if c in ['(','[','{']:                stack.append(c)            else:                if(len(stack)==0):                    return False                top=stack[len(stack)-1]                if ((c == ')' and top=='(') or (c == ']' and top=='[') or (c == '}' and top == '{')):                    stack.pop()                else:                    return False        return len(stack)==0

成绩：
43ms,beats 55.57%,众数40ms,27.91%