java
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
if(root1==null)return root2;
if(root2==null)return root1;
root1.val+=root2.val;//直接修改root1
root1.left=mergeTrees(root1.left,root2.left);
root1.right=mergeTrees(root1.right,root2.right);
return root1;
}
}