101. Symmetric Tree

def isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        queue = [root]
        while queue:
            values = [i.val if i else None for i in queue]
            if values != values[::-1]: return False
            queue = [child for i in queue if i for child in (i.left, i.right)]
        return True

def isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        if root is None:
            return True
        return self.helper(root.left, root.right)

    def helper(self, left, right):
        if not left or not right:
            return left == right
        return left.val == right.val and self.helper(left.left, right.right) and self.helper(left.right, right.left)