class Solution:
def isSymmetric(self, root):
"""
:type root: TreeNode
:rtype: bool
"""
def helper(root, mirror):
if not root and not mirror:
return True
if root and mirror and root.val == mirror.val:
return helper(root.left, mirror.right) and helper(root.right, mirror.left)
return False
return helper(root, root)
将二叉树root复制为二叉树root和二叉树mirror,然后比较root.val and mirror.val 以及root.left and mirror.right 以及 root.right and mirror.left 是否相等,若全部相等则return ture反之return false