LeetCode617. 合并二叉树 [简单]

我的题解：

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        if(t1&&t2){
            t1->val+=t2->val;
            t1->left=mergeTrees(t1->left,t2->left);
            t1->right=mergeTrees(t1->right,t2->right);
            return t1;
        }
        else if(!t1 && t2)  return t2;
        else if(t1 &&!t2)   return t1;
        else    return NULL;
    }
};