题目链接/文章讲解：https://programmercarl.com/0617.%E5%90%88%E5%B9%B6%E4%BA%8C%E5%8F%89%E6%A0%91.html

视频讲解：https://www.bilibili.com/video/BV1m14y1Y7JK

CPP

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), 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;

        root1->left = mergeTrees(root1->left , root2->left);
        root1->right = mergeTrees(root1->right , root2->right);
        return root1;
    }
};