'''
Description: 
Autor: Au3C2
Date: 2021-03-22 16:36:59
LastEditors: Au3C2
LastEditTime: 2021-03-22 16:38:09
'''
class Solution:
	def isSymmetric(self, root):
		"""
		:type root: TreeNode
		:rtype: bool
		"""
		if not root:
			return True
		def dfs(left,right):
			# 递归的终止条件是两个节点都为空
			# 或者两个节点中有一个为空
			# 或者两个节点的值不相等
			if not (left or right): # 都为空返回True
				return True
			if not (left and right): # 有一个为空返回False
				return False 
			if left.val!=right.val: # 值不相等返回False
				return False
			return dfs(left.left,right.right) and dfs(left.right,right.left)
		# 用递归函数，比较左节点，右节点
		return dfs(root.left,root.right)

树 简单

https://leetcode-cn.com/problems/symmetric-tree/