leetcode_ valid parentheses

20. Valid Parentheses

Given a string consisting only of '(', ')', '{', '}', '[', ']', check whether the string is valid.

A valid string must satisfy:

• An opening bracket must be closed with a closing bracket of the same type.
• Opening parentheses must be closed in the correct order.

Note that an empty string is considered a valid string.

Algorithm ideas: the use of stack
python code

class Solution:
    def isValid(self, s: str) -> bool:
        t = []
        for i in s:
            if i == "(" or i == "{" or i == "[":
                t.append(i)
            elif i == ")":
                if len(t) == 0 or t.pop() != "(":
                    return False
            elif i == "}":
                if len(t) == 0 or t.pop() != "{":
                    return False
            elif i == "]":
                if len(t) == 0 or t.pop() != "[":
                    return False
        if len(t) == 0:
            return True
        else:
            return False