1class Node {
2    constructor(val) {
3        this.val = val;
4        this.next = null;
5        this.prev = null;
6    }
7}
8
9class MyLinkedList {
10    constructor() {
11        this.head = null;
12    }
13
14    get(index) {
15        let current = this.head;
16        for (let i = 0; i < index; i++) {
17            if (!current) return -1;
18            current = current.next;
19        }
20        return current ? current.val : -1;
21    }
22
23    addAtHead(val) {
24        const node = new Node(val);
25        node.next = this.head;
26        if (this.head) this.head.prev = node;
27        this.head = node;
28    }
29
30    addAtTail(val) {
31        const node = new Node(val);
32        if (!this.head) {
33            this.head = node;
34            return;
35        }
36        let current = this.head;
37        while (current.next) {
38            current = current.next;
39        }
40        current.next = node;
41        node.prev = current;
42    }
43
44    addAtIndex(index, val) {
45        if (index === 0) {
46            this.addAtHead(val);
47            return;
48        }
49        let current = this.head;
50        for (let i = 0; i < index - 1; i++) {
51            if (!current) return;
52            current = current.next;
53        }
54        if (current) {
55            const node = new Node(val);
56            node.next = current.next;
57            if (current.next) current.next.prev = node;
58            current.next = node;
59            node.prev = current;
60        }
61    }
62
63    deleteAtIndex(index) {
64        let current = this.head;
65        for (let i = 0; i < index && current; i++) {
66            current = current.next;
67        }
68        if (!current) return;
69        if (current.prev) current.prev.next = current.next;
70        else this.head = current.next;
71        if (current.next) current.next.prev = current.prev;
72    }
73}