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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
    def isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        if root == None:
            return True
        return self.check(root.left, root.right)
    def check(self, node1, node2):
        if node1 == None and node2 == None:
            return True
        elif node1 == None or node2 == None:
            return False
        else:
            cond1 = node1.val == node2.val
            cond2 = self.check(node1.right, node2.left)
            cond3 = self.check(node1.left, node2.right)
            return cond1 and cond2 and cond3