Valid Parentheses

LeetCode 20

class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """
        """
        Time Complexity: O(n^2) because str.replace: O(n)
        
        也可以利用老方法 stack
        """
        while '()' in s or '{}' in s or '[]' in s:
            s = s.replace('{}','').replace('()','').replace('[]','')        
        return s == '':