力扣 20. 有效的括号

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def isValid(s):
    if not s: return True 
    pip = {"}": "{",
           ")": "(",
           "]": "["}

    queue = []

    for sign in s:
        if sign in pip.keys():
            if not queue:
                return False
            else:
                cur = queue.pop()
                if pip[sign] != cur:
                    return False
        else:
            queue.append(sign)
        
    
    if not queue:
        return True
    else:
        return False