Valid Parentheses

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.

Example 1:

Input: s = "()"
Output: true

Example 2:

Input: s = "()[]{}"
Output: true

Example 3:

Input: s = "(]"
Output: false

Constraints:

• 1 <= s.length <= 104
• s consists of parentheses only '()[]{}'.

SOLUTION:

class Solution:
    def isValid(self, s: str) -> bool:
        stack = []
        validPairs = ['()', '[]', '{}']
        valid = True
        for bracket in s:
            if bracket in [b[0] for b in validPairs]:
                stack.append(bracket)
            else:
                if len(stack) > 0:
                    if (stack.pop() + bracket) not in validPairs:
                        valid = False
                        break
                else:
                    valid = False
                    break
        if len(stack) > 0:
            valid = False
        return valid