class TreeNode{
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int x){
            val = x ;
        }
}    
public class MirrorBinaryTree {
    public void Mirror(TreeNode root) {
        TreeNode tempNode;
        if (root == null){
            return;
        }
        if (root.left == null && root.right == null) return;

        tempNode = root.left;
        root.left = root.right;
        root.right = tempNode;
        if (root.left!=null) Mirror(root.left);
        if (root.right!=null) Mirror(root.right);
    }