leetcode101 对称二叉树

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    def isSymmetric(self, root):
        if root is None:
            return True
        return self.help(root.left, root.right) 

    def help(self, left, right):
        ’‘’
        终止条件是左子树和右子树是叶子节点的时候
        ‘’‘
        if not left and not right:
            return True
        if not left:
            return False
        if not right:
            return False
        if left.val != right.val:
            return False

        return self.help(left.left, right.right) and self.help(right.left, left.right)