Invert Binary Tree

Invert a binary tree.

Example

  1         1
 / \       / \
2   3  => 3   2
   /       \
  4         4

1 /**
 2  * Definition of TreeNode:
 3  * public class TreeNode {
 4  *     public int val;
 5  *     public TreeNode left, right;
 6  *     public TreeNode(int val) {
 7  *         this.val = val;
 8  *         this.left = this.right = null;
 9  *     }
10  * }
11  */
12 public class Solution {
13     /**
14      * @param root: a TreeNode, the root of the binary tree
15      * @return: nothing
16      */
17     public void invertBinaryTree(TreeNode root) {
18         // write your code here
19         if (root == null) return;
20         
21         TreeNode left = root.left;
22         root.left = root.right;
23         root.right = left;
24         
25         invertBinaryTree(root.left);
26         invertBinaryTree(root.right);
27     }
28 }