题目链接：https://leetcode-cn.com/problems/dui-cheng-de-er-cha-shu-lcof/
难度：简单

描述：
请实现一个函数，用来判断一棵二叉树是不是对称的。如果一棵二叉树和它的镜像一样，那么它是对称的。

题解

  1. # Definition for a binary tree node.
  2. # class TreeNode:
  3. #     def __init__(self, x):
  4. #         self.val = x
  5. #         self.left = None
  6. #         self.right = None
  8. class Solution:
  9.     def isSymmetric(self, root: TreeNode) -> bool:
  10.         def recursion(l, r):
  11.             if l is None and r is None:
  12.                 return True
  13.             if l is None or r is None or l.val != r.val:
  14.                 return False
  15.             return recursion(l.left, r.right) and recursion(l.right, r.left)
  17.         if root is None:
  18.             return True
  20.         return recursion(root.left, root.right)