代码：
def isValid( s):
    dic = {'(': ')', '{': '}', '[': ']', '?': '?'}
    stack = ['?']
    for x in s:
        if x in dic:
            stack.append(x)
        elif dic[stack.pop()] != x:
            return False
    return len(stack) == 1

s='{}{()'
print(isValid(s))