剑指offer（Python）面试题28-对称的二叉树

题目描述
请实现一个函数，用来判断一颗二叉树是不是对称的。注意，如果一个二叉树同此二叉树的镜像是同样的，定义其为对称的。

     1
    /  \
   2    2
  / \  / \
 3  4  4  3

思路：

• 根节点为空的二叉树也是对称二叉树
• self.isSymBT(tree1.left,tree2.right) and self.isSymBT(tree1.right,tree2.left)
  python代码：

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    def isSymmetrical(self, pRoot):
        # write code here
        if not pRoot:  
            return True
        return self.isSymBT(pRoot.left,pRoot.right)
    def isSymBT(self,tree1,tree2):
        if tree1 == None and tree2 == None:
            return True
        if tree1 == None or tree2 == None:
            return False
        if tree1.val != tree2.val:
            return False
        else:
            return self.isSymBT(tree1.left,tree2.right) and self.isSymBT(tree1.right,tree2.left)