20. Valid Parentheses.py

class Solution(object):
    def isValid(self, s):
        """
        :type s: str
        :rtype: bool
        """

        stack = []

        for i in s:
            if(i=="["):
                stack.append("]")
            elif(i=="{"):
                stack.append("}")
            elif(i=="("):
                stack.append(")")
            else:
                if stack:
                    if(stack.pop()!=i):
                        return False
                else:
                    return False
        return not any(stack)