LeetCode 226 Invert Binary Tree

     4
   /     2     7
 / \   / 1   3 6   9

     4
   /     7     2
 / \   / 9   6 3   1

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