二叉树的镜像

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

        if(root.left!=null||root.right!=null){
            TreeNode tmp = root.left;
            root.left = root.right;
            root.right = tmp;
            mirrorTree(root.left);
            mirrorTree(root.right);
        }
        return root;

    }
}