ListNode* mergeKLists(vector<ListNode*>& lists) {

         vector<ListNode*> p;

         for (vector<ListNode*>::iterator it = lists.begin(); it != lists.end(); it++) {

             if (*it != NULL){

                 ListNode *pn = *it;

                 p.push_back(pn);

             }

         }

         if (p.size() == )

             return NULL;

         ListNode *dummy = new ListNode();

         ListNode *pn = dummy;

         while (p.size() > ) {

             int n = minval(p);

             pn->next = p[n];

             pn = pn->next;

             p[n] = p[n]->next;

             if (p[n] == NULL)

                 p.erase(p.begin() + n);

         }

         return dummy->next;

     }

     int minval(vector<ListNode*> p)

     {

         auto res = p.begin();

         for (auto it = p.begin(); it != p.end(); it++) {

             if ((*it)->val <= (*res)->val)

                 res = it;

         }

         return res - p.begin();

     }