【leetcode】合并二叉树

struct TreeNode* mergeTrees(struct TreeNode* t1, struct TreeNode* t2){
    if(t1==NULL&&t2!=NULL) return t2;
   
    else if(t2==NULL&&t1!=NULL) return t1;

    else if(t1==NULL&&t2==NULL) return NULL;

    else t1->val=t1->val+t2->val;

    t1->left=mergeTrees(t1->left,t2->left);
    t1->right=mergeTrees(t1->right,t2->right);
    return t1;
}