1var assert = require('assert');
2
3function detectLoop(head) {
4  let pointer1, pointer2;
5  pointer1 = head;
6  pointer2 = head;
7
8  while (pointer2.next.next) {
9    pointer1 = pointer1.next;
10    pointer2 = pointer2.next.next;
11
12    if (pointer1 == pointer2) {
13      return true;
14    }
15  }
16  return false;
17}
18
19function Node(val) {
20  this.val = val;
21  this.next = null;
22}
23
24function LinkedListNode(val) {
25  this.val = val;
26  this.next = null;
27}
28
29var list1 = new LinkedListNode(3);
30var nodes1 = [4, 5, 6, 7, 8, 9, 10];
31createNodes(list1, nodes1);
32
33var list2 = new LinkedListNode(1);
34var nodes2 = [2, 3, 4, 5, 6, 7, 8];
35createNodes(list2, nodes2);
36
37function createNodes(head, nodes) {
38  for (let i = 0; i < nodes.length; i++) {
39    var newNode = new LinkedListNode(nodes[i]);
40    head.next = newNode;
41    head = newNode;
42  }
43}
44
45try {
46  list1.next.next.next.next.next.next = list1.next.next;
47  assert.equal(detectLoop(list1), true);
48
49  console.log(
50    'PASSED: Assuming list1.head.next.next.next.next = list1.head, we can detect an artificial loop in the linked list'
51  );
52} catch (err) {
53  console.log(err);
54}