LeetCode 226. Invert Binary Tree （反转二叉树）

Invert a binary tree.

     4
   /     2     7
 / \   / 1   3 6   9

to

     4
   /     7     2
 / \   / 9   6 3   1

Trivia:
This problem was inspired by this original tweet by Max Howell:

Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so fuck off.

　　这道题目给了我们一个二叉树，让我们把它反转一下。对于每一个点，它的左边和右边子树需要对调一下。利用postOrder 来遍历树，当走到最低端的时候，点 == null， 返回null， 对于每一个点，把它的left 和right 互换一下。return 这个点。

Java Solution:

Runtime beats 27.97%

完成日期：07/04/2017

关键词：Tree

关键点：把left 和right 互换

 1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution
11 {
12     public TreeNode invertTree(TreeNode root)
13     {
14         if(root == null)
15             return null;
16
17         // continue children
18         invertTree(root.left);
19         invertTree(root.right);
20
21         // swap left and right
22         TreeNode temp;
23         temp = root.left;
24         root.left = root.right;
25         root.right = temp;
26
27         return root;
28     }
29 }

参考资料：N/A