20. Valid Parentheses

1class Solution:
2    def isValid(self, s: str) -> bool:
3        stack = []
4        pairs = {')': '(', ']': '[', '}': '{'}
5        for char in s:
6            if char in pairs:
7                if stack and stack[-1] == pairs[char]:
8                    stack.pop()
9                else:
10                    return False
11            else:
12                stack.append(char)
13        return not stack