merge-two-sorted-lists.js

const mergeTwoLists = (list1, list2) => {
  if (!list1 || !list2) return list1 || list2;

  if (list1.val < list2.val) {
    list1.next = mergeTwoLists(list1.next, list2);
    return list1;
  } else {
    list2.next = mergeTwoLists(list1, list2.next);
    return list2;
  }
};