circularLinkedList.js

/**
 * Given a Linked List , Return True If list is Circular or Not
 */

class Node {
    constructor(data, next = null) {
        this.data = data;
        this.next = next
    }
}

class CircularLinkedList {
    constructor() {
        this.head = null;
    }

    insertFirst(data) {
        this.head = new Node(data, this.head);
    }

    sizeOfList() {
        let count = 0;
        let firstNode = this.head;
        while (this.head != null) {
            this.head = this.head.next;
            count++;
        }
        this.head = firstNode;
        return count;
    }

    makeCircular() {
        let firstNode = this.head;
        while (this.head.next != null) {
            this.head = this.head.next
        }

        this.head.next = firstNode;
    }

    checkIfCircular() {
        let slow = this.head;
        let fast = this.head.next;
        while (slow && fast) {
            slow = slow.next;
            fast = fast.next.next;
            if (slow == fast)
                return true;
        }
        return false;
    }
}

const nodeOne = new Node(89);
let list = new CircularLinkedList();
list.head = nodeOne;
list.insertFirst(3);
list.insertFirst(5);
list.insertFirst(6);
list.insertFirst(3);
list.insertFirst(5);
list.insertFirst(6);
list.insertFirst(3);
list.insertFirst(5);
list.insertFirst(6);
list.insertFirst(3);
list.insertFirst(5);
list.insertFirst(88);

list.makeCircular();

console.log(list.checkIfCircular());