LeetCode: Partition List Solution

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} head
10 * @param {number} x
11 * @return {ListNode}
12 */
13// not fair way
14var partition = function (head, x) {
15  const arr = []
16
17  while (head) {
18    arr.push(head.val)
19    head = head.next
20  }
21
22  const nodes = [...arr.filter(el => el < x), ...arr.filter(el => el >= x)].map(
23    el => new ListNode(el)
24  )
25
26  for (let i = 0; i < nodes.length - 1; i++) {
27    nodes[i].next = nodes[i + 1]
28  }
29
30  return nodes[0] || null
31}
32
33var partition = function (head, x) {
34  let [dummy1, dummy2] = [new ListNode(0), new ListNode(0)]
35  let [newHead1, newHead2] = [dummy1, dummy2]
36  while (head) {
37    if (head.val < x) {
38      dummy1 = dummy1.next = head
39    } else {
40      dummy2 = dummy2.next = head
41    }
42    head = head.next
43  }
44  dummy2.next = null // avoid cyclic
45  dummy1.next = newHead2.next
46  newHead1 = newHead1.next
47  return newHead1
48}