Flatten a Multilevel Doubly Linked List LeetCode solution in JavaScript

1
var flatten = function (head) {
2
  var arr = [];
3
  var temp = head;
4
  var prev = null;
5
  while (temp) {
6
    if (temp.child != null) {
7
      arr.push(temp.next);
8
      temp.next = temp.child;
9
      temp.child.prev = temp;
10
      temp.child = null;
11
    }
12
    prev = temp;
13
    temp = temp.next;
14
  }
15
  for (var j = arr.length - 1; j >= 0; j--) {
16
    if (arr[j] != null) mergeOtherLists(arr[j]);
17
  }
18
  return head;
19

20
  function mergeOtherLists(root) {
21
    prev.next = root;
22
    root.prev = prev;
23
    while (root) {
24
      prev = root;
25
      root = root.next;
26
    }
27
  }
28
};