[leetcode]Valid Parentheses @ Python

原题地址:https://oj.leetcode.com/problems/valid-parentheses/

题意:

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.

解题思路:判断括号匹配的合法性。使用一个栈来解决问题。遇到左括号入栈,遇到右括号,检查栈顶的左括号是否匹配,如果匹配,弹栈,如果不匹配,返回错误。如果栈为空,而遇到右括号,同样返回错误。遍历完后,栈如果不空,同样返回错误。

代码:

class Solution:
    # @return a boolean
    def isValid(self, s):
        stack = []
        for i in range(len(s)):
            if s[i] == '(' or s[i] == '[' or s[i] == '{':
                stack.append(s[i])
            if s[i] == ')':
                if stack == [] or stack.pop() != '(':
                    return False
            if s[i] == ']':
                if stack == [] or stack.pop() != '[':
                    return False
            if s[i] == '}':
                if stack == [] or stack.pop() != '{':
                    return False
        if stack:
            return False
        else:
            return True

 

posted @ 2014-06-10 12:58  南郭子綦  阅读(5370)  评论(1编辑  收藏  举报