0020 有效的括号

class Solution:
    def isValid(self, s: str) -> bool:
        stk = []
        d = {'()', '[]', '{}'}
        for c in s:
            if c in '({[':
                stk.append(c)
            elif not stk or stk.pop() + c not in d:
                return False
        return not stk

if __name__ == "__main__":
    sol = Solution()
    print(sol.isValid("()"))      # True
    print(sol.isValid("()[]{}"))  # True
    print(sol.isValid("(]"))      # False
    print(sol.isValid("([)]"))    # False
    print(sol.isValid("{[]}"))    # True
    print(sol.isValid("("))       # False