20. Valid Parentheses leetcode Python 2016 new Season

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本文介绍了一种使用栈数据结构来验证包含括号的字符串是否有效的方法。文章详细解释了如何通过遍历输入字符串并利用栈来跟踪括号的开闭情况，以此判断括号是否正确配对。

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.

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need O(n) time to go through the whole array and worst case O(n) space to store the array.

class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        stack = []
        for index in range(len(s)):
            current_string = s[index]
            if current_string == '(' or current_string == '[' or current_string == '{':
                stack.append(current_string)
            if current_string == ')':
                if not stack or stack.pop() != '(':
                    return False
            if current_string == ']':
                if not stack or stack.pop() != '[':
                    return False
            if current_string == '}':
                if not stack or stack.pop() != '{':
                    return False
        if stack:
            return False
        return True