linkedListCycle.js

//////////////////////////////////////////////Linked List Cycle/////////////////////////////////////////////////
// Given head, the head of a linked list, determine if the linked list has a cycle in it.
// There is a cycle in a linked list if there is some node in the list that can be reached again by continuously following
// the next pointer. Internally, pos is used to denote the index of the node that tail's next pointer is connected to. Note that pos is not passed as a parameter.
// Return true if there is a cycle in the linked list. Otherwise, return false.
// Example 1:
// Input: head = [3,2,0,-4], pos = 1
// Output: true
// Explanation: There is a cycle in the linked list, where the tail connects to the 1st node (0-indexed).
// Example 2:
// Input: head = [1,2], pos = 0
// Output: true
// Explanation: There is a cycle in the linked list, where the tail connects to the 0th node.
// Example 3:
// Input: head = [1], pos = -1
// Output: false
// Explanation: There is no cycle in the linked list.
// Constraints:
//
// The number of the nodes in the list is in the range [0, 104].
// -105 <= Node.val <= 105
// pos is -1 or a valid index in the linked-list.
// Follow up: Can you solve it using O(1) (i.e. constant) memory?
/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

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

    while(fast != null && fast.next != null){
        fast = fast.next.next
        slow = slow.next
        if(fast === slow) return true
    }
    return false
};

// console.log(hasCycle([3,2,0,-4]));
// console.log(hasCycle([1, 2]));
// console.log(hasCycle([1]));