cpp

static ListNode *reverse(ListNode *head, int k) {
    // TODO: Write your code here
    ListNode * dummy = new ListNode(-1);
    dummy->next = head;
    ListNode * prev = dummy;
    ListNode * cur = head;
    ListNode * last_node_of_prev_list = prev;
    ListNode * last_node_of_cur_list = cur;

    while (cur) {
      int i = 0;
      
      // reverse linked list
      while (cur && i < k) {
        ListNode* nextnode = cur->next;
        cur->next = prev;
        prev = cur;
        cur = nextnode;
        i++;
      }

      // reset pointers
      last_node_of_prev_list->next = prev;
      last_node_of_cur_list->next = cur;

      // update pointers
      last_node_of_prev_list = last_node_of_cur_list;
    last_node_of_cur_list = cur;
    }
    return dummy->next;
  }
};

int main(int argc, char *argv[]) {
  ListNode *head = new ListNode(1);
  head->next = new ListNode(2);
  head->next->next = new ListNode(3);
  head->next->next->next = new ListNode(4);
  head->next->next->next->next = new ListNode(5);
  head->next->next->next->next->next = new ListNode(6);
  head->next->next->next->next->next->next = new ListNode(7);
  head->next->next->next->next->next->next->next = new ListNode(8);

  ListNode *result = ReverseEveryKElements::reverse(head, 3);
  cout << "Nodes of the reversed LinkedList are: ";
  while (result != nullptr) {
    cout << result->value << " ";
    result = result->next;
  }
}