leetcode 20. Valid parentheses (python3) 36 ms

Title description:

Given a string consisting only of '(', ')', '{', '}', '[', ']', check whether the string is valid.
A valid string needs to satisfy:
the opening parenthesis must be closed with the same type of closing parenthesis.
Opening parentheses must be closed in the correct order.
Note that an empty string is considered a valid string.

Example one:

Input: "()"
Output: true

Example two:

Input: “()[]{}”
Output: true

Example three:

Input: "(]"
Output: false

Example four:

Input: “([)]”
Output: false

Example five:

Input: “{[]}”
Output: true

Problem-solving ideas:

class Solution:
    def isValid(self, s: str) -> bool:
        output = []
        label = {')':'(', '}':'{', ']':'['}
        for idx in range(len(s)):
            if s[idx] in ['(', '{', '[']:
                output.append(s[idx])
            elif s[idx] in [')', '}', ']'] and len(output) == 0:
                return False
            elif s[idx] in [')', '}', ']'] and label[s[idx]] == output[-1]:
                output.pop()
            else:
                return False
        if len(output) != 0:
            return False
        else:
            return True

Performance analysis: