LeetCode: Linked List Cycle Solution

Approach

Set the visited state for each node, if revisit a visited node, then the list contains cycle

Implementation

1/**
2 * Definition for singly-linked list.
3 * function ListNode(val) {
4 *     this.val = val;
5 *     this.next = null;
6 * }
7 */
8
9/**
10 * @param {ListNode} head
11 * @return {boolean}
12 */
13var hasCycle = function (head) {
14  if (!head) {
15    return false
16  }
17  if (head.visited) {
18    return true
19  }
20  head.visited = true
21  return hasCycle(head.next)
22}