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.

题目标签：Tree

　　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

 /**
  * Definition for a binary tree node.
  * public class TreeNode {
  *     int val;
  *     TreeNode left;
  *     TreeNode right;
  *     TreeNode(int x) { val = x; }
  * }
  */
 public class Solution
 {
     public TreeNode invertTree(TreeNode root)
     {
         if(root == null)
             return null;         // continue children
         invertTree(root.left);
         invertTree(root.right);         // swap left and right
         TreeNode temp;
         temp = root.left;
         root.left = root.right;
         root.right = temp;         return root;
     }
 }

参考资料：N/A

LeetCode 算法题目列表 – LeetCode Algorithms Questions List