翻轉一棵二叉樹。

示例：

輸入：

     4
   /     2     7
 / \   / 1   3 6   9

輸出：

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

226. 翻轉二叉樹python