Valid Parentheses

LeetCode 20 · View on LeetCode

Push opening brackets onto a stack. For each closing bracket, check if it matches the top. Valid if the stack is empty at the end.

def is_valid(s: str) -> bool:
    stack = []
    pairs = {')': '(', ']': '[', '}': '{'}
    for ch in s:
        if ch in pairs:
            if not stack or stack[-1] != pairs[ch]:
                return False
            stack.pop()
        else:
            stack.append(ch)
    return not stack

if __name__ == '__main__':
    print(is_valid("()"))      # True
    print(is_valid("()[]{}"))  # True
    print(is_valid("(]"))      # False
    print(is_valid("([)]"))    # False
    print(is_valid("{[]}"))    # True