public class Solution {
public TreeNode mergeTrees (TreeNode t1, TreeNode t2) {
// write code here
if(t1==null || t2==null){
return t1==null?t2:t1;
}
t1.val = t1.val + t2.val;
t1.left = mergeTrees(t1.left, t2.left);
t1.right = mergeTrees(t1.right, t2.right);
return t1;
}
}