考前佛脚：leetcode第三弹

    def isValid(s):
        s = list(s)

        sym_dict = {")": "(", "}": "{", "]":"["}

        stack =[]
        close = []
        
        if len(s)%2 == 0:
            for i in range(len(s)):
                if s[i] in sym_dict.values():
                    stack.append(s[i])
                if s[i] in sym_dict.keys() and stack != [] and stack[-1] == sym_dict[s[i]]:
                    close.append(stack.pop())
            if stack == [] and len(close) == len(s)/2:
                return True
        return False