merge k sort list.cpp

class Solution
{
public:
     ListNode *mergeKLists(vector<ListNode *> &lists)
     {

          if (lists.empty())
               return NULL;

          vector<int> vect;
          for (int i = 0; i < lists.size(); i++)
          {
               if (lists[i] == nullptr)
                    continue;
               vector<int> mtx;
               ListNode *temp = lists[i];

               while (temp != nullptr)
               {
                    mtx.push_back(temp->val);
                    temp = temp->next;
               }

               vect.insert(vect.end(), mtx.begin(), mtx.end());
          }

          if (vect.empty())
               return nullptr;

          sort(vect.begin(), vect.end());

          ListNode *root = new ListNode(vect[0]);

          ListNode *curr = root;

          for (int i = 1; i < vect.size(); i++)
          {
               ListNode *temp = new ListNode(vect[i]);
               curr->next = temp;

               curr = curr->next;
          }

          return root;
     }
};
//  leetcode  - 23