designLL.js

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

class MyLinkedList  {
    constructor() {
        this.head = new Node();
        this.tail = new Node();
        this.length = 0;
        this.head.next = this.tail;
        this.tail.prev = this.head;
    }

    get(idx) {
        if(idx < 0 || idx >= this.length) return -1;
        let curr = this.head.next;
        while(idx--) curr=curr.next;
        return curr.val
    }

    addAtHead(val) {
        let prev = this.head;
        let next = this.head.next;

        let node = new Node(val, prev, next);
        prev.next = node;
        next.prev = node;

        this.length++;
    }

    addAtTail(val) {
        let prev = this.tail.prev;
        let next = this.tail;
        let node = new Node(val, prev, next);
        prev.next = node;
        next.prev = node;
        this.length++;
    }
    addAtIndex(idx, val) {
        if(idx<0|| idx > this.length) return null;
        if(idx === this.length) {
            this.addAtTail(val);
            return;
        }
        let prev = this.head;
        while(idx--) prev = prev.next;
        let next = prev.next;

        let node = new Node(val, prev, next);
        prev.next = node;
        next.prev = node;
        this.length++;
    }
    deleteAtIndex(idx) {
        if(idx < 0 || idx >= this.length) return null;
        let prev = this.head;
        while(idx--) prev = prev.next;
        let next = prev.next.next;
        prev.next = next;
        next.prev = prev;
        this.length--;
    }
}