0141_linked_list_cycle_(easy).js

/**
 * 141. Linked List Cycle
 *
 * https://leetcode.com/problems/linked-list-cycle/
 *
 * Given a linked list, determine if it has a cycle in it.
 *
 * Follow up:
 * Can you solve it without using extra space?
 */

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

/**
 * @param {ListNode} head
 * @return {boolean}
 */
const hasCycle = (head) => {
  let slow = head;
  let fast = head;

  while (fast && fast.next) {
    slow = slow.next;
    fast = fast.next.next;

    if (slow === fast) {
      return true;
    }
  }

  return false;
};

export { hasCycle };