/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 * };
 */

class Solution {
public:
    /**
     * 
     * @param t1 TreeNode类 
     * @param t2 TreeNode类 
     * @return TreeNode类
     */
    TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        // write code here
        if(!t1) return t2;
        if(!t2) return t1;
        t1->val+=t2->val;
        t1->left=mergeTrees(t1->left, t2->left);
        t1->right=mergeTrees(t1->right, t2->right);
        return t1;

    }
};

递归思路解决;

总体来看,还是将t2连接到t1上。