Merge Two Sorted Lists LeetCode solution in JavaScript

1
/**
2
 * Definition for singly-linked list.
3
 * function ListNode(val, next) {
4
 * this.val = (val===undefined ? 0 : val)
5
 * this.next = (next===undefined ? null : next)
6
 * }
7
 */
8
/**
9
 * @param {ListNode} list1
10
 * @param {ListNode} list2
11
 * @return {ListNode}
12
 */
13
var mergeTwoLists = function (list1, list2) {
14
  if (!list1) return list2;
15
  if (!list2) return list1;
16

17
  let mergedList = new ListNode(0);
18
  let ptr = mergedList;
19
  let curr1 = list1;
20
  let curr2 = list2;
21

22
  while (curr1 && curr2) {
23
    let newNode = new ListNode();
24
    if (!curr2 || curr1.val < curr2.val) {
25
      newNode.val = curr1.val;
26
      newNode.next = null;
27
      ptr.next = newNode;
28
      curr1 = curr1.next;
29
    } else {
30
      newNode.val = curr2.val;
31
      newNode.next = null;
32
      ptr.next = newNode;
33
      curr2 = curr2.next;
34
    }
35

36
    ptr = ptr.next;
37
  }
38

39
  if (curr1 !== null) {
40
    ptr.next = curr1;
41
    curr1 = curr1.next;
42
  }
43

44
  if (curr2 !== null) {
45
    ptr.next = curr2;
46
    curr2 = curr2.next;
47
  }
48

49
  return mergedList.next;
50
};