Algorithms for Interview 1: Stack

LeetCode 20 Valid Parentheses.py

class Solution:
    def isValid(self, s: str) -> bool:
        mapping = {')': '(', ']': '[', '}': '{'}
        stack = []
        for char in s:
            if mapping.get(char):
                if not stack:
                    return False
                else:
                    if stack[-1] == mapping[char]:
                        stack.pop()
                    else:
                        return False
            else:
                stack.append(char)
        return not stack