/**

 public class TreeNode {

     int val = 0;

     TreeNode left = null;

     TreeNode right = null;

     public TreeNode(int val) {

         this.val = val;

     }

 }

 */

 public class Solution {

     public void Mirror(TreeNode root) {

         if(root == null) return;

         swap(root);

         if(root.left!=null) Mirror(root.left);

         if(root.right!=null)Mirror(root.right);

     }

     private void swap(TreeNode root){

         TreeNode t = root.left;

         root.left = root.right;

         root.right = t;

     }

 }