翻转一棵二叉树。
示例：
输入：
4 / 2 7 / \ / 1 3 6 9
输出：
4 / 7 2 / \ / 9 6 3 1
# Definition for a binary tree node.
# class TreeNode:
# def __init__(self, x):
# self.val = x
# self.left = None
# self.right = None
class Solution:
def invertTree(self, root):
"""
:type root: TreeNode
:rtype: TreeNode
"""
if root == None:
return root
temp = root.left
root.left = root.right
root.right = temp
self.invertTree(root.left)
self.invertTree(root.right)
return root
原文：https://www.cnblogs.com/zyjdbk/p/9646353.html