function solution(l, k) {
  let dummyHead = new ListNode(-1);
  let connector = dummyHead;

  let prev, curr, next, tempTail;

  dummyHead.next = l;

  prev = null;
  curr = l;
  let stepsCounter = 0;
  while (curr) {
    stepsCounter = 0;
    tempTail = curr;
    for (; stepsCounter < k && curr; ++stepsCounter) {
      next = curr.next;
      curr.next = prev;
      prev = curr;
      curr = next;
    }
    connector.next = prev;
    tempTail.next = curr;
    connector = tempTail;
  }
  return dummyHead.next;
}