1  public TreeNode mirrorTree(TreeNode root) {
 2          if(root==null){
 3             return null;
 4         }else if (root.left!=null||root.right != null){
 6             if (root.right==null){
 7                 root.left=mirrorTree(root.left);
 8                 TreeNode treeNode = new TreeNode(root.left.val);
 9                 treeNode.left=root.left.left;
10                 treeNode.right=root.left.right;
11                 root.left=root.right;
12                 root.right=treeNode;
13             }else if (root.left == null) {
14                
15                 root.right=mirrorTree(root.right);
16                 TreeNode treeNode = new TreeNode(root.right.val);
17                 treeNode.left=root.right.left;
18                 treeNode.right=root.right.right;
19                 root.right=root.left;
20                 root.left=treeNode;
21             }else {
22                 root.left=mirrorTree(root.left);
23                 root.right=mirrorTree(root.right);
24                 TreeNode treeNode = new TreeNode(root.right.val);
25                 treeNode.left=root.right.left;
26                 treeNode.right=root.right.right;
27                 root.right=root.left;
28                 root.left=treeNode;
29             }
30         }else {
31             return root;
32         }
33         return root;
34     }