1 /**
 2  * Definition for a binary tree node.
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 class Solution {
11     public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
12         if(t1!=null&&t2!=null) t1.val=t1.val+t2.val;
13         if(t1==null&&t2!=null){
14             t1=new TreeNode(t2.val);
15         }
16         if(t2!=null){
17             t1.left=mergeTrees(t1.left,t2.left);
18             t1.right=mergeTrees(t1.right,t2.right);
19         }
20         return t1;
21     }
22 }