class Solution(object):
def isSymmetric(self, root):
"""
:type root: TreeNode
:rtype: bool
"""
def helper(p, q):
if not p and not q:
return True
if not p or not q:
return False
if p.val == q.val:
return helper(p.left, q.right) and helper(p.right, q.left)
else:
return False
return helper(root, root)
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