1class Node:
2    def __init__(self, val: int):
3        self.val = val
4        self.next = None
5
6class MyLinkedList:
7    def __init__(self):
8        self.head = None
9
10    def get(self, index: int) -> int:
11        current = self.head
12        for i in range(index):
13            if current is None:
14                return -1
15            current = current.next
16        return current.val if current else -1
17
18    def addAtHead(self, val: int) -> None:
19        node = Node(val)
20        node.next = self.head
21        self.head = node
22
23    def addAtTail(self, val: int) -> None:
24        node = Node(val)
25        if not self.head:
26            self.head = node
27        else:
28            current = self.head
29            while current.next:
30                current = current.next
31            current.next = node
32
33    def addAtIndex(self, index: int, val: int) -> None:
34        if index == 0:
35            self.addAtHead(val)
36            return
37        current = self.head
38        for i in range(index - 1):
39            if current is None:
40                return
41            current = current.next
42        if not current: return
43        node = Node(val)
44        node.next = current.next
45        current.next = node
46
47    def deleteAtIndex(self, index: int) -> None:
48        if index == 0:
49            if self.head:
50                self.head = self.head.next
51            return
52        current = self.head
53        for i in range(index - 1):
54            if current is None:
55                return
56            current = current.next
57        if current and current.next:
58            current.next = current.next.next

1
    private class Node {
        public int val;
        public Node next;
        public Node prev;
        public Node(int _val) { val = _val; }
    }

    private Node head;

    public MyLinkedList() {
        head = null;
    }

    public int Get(int index) {
        Node current = head;
        for (int i = 0; i < index && current != null; i++) {
            current = current.next;
        }
        return current == null ? -1 : current.val;
    }

    public void AddAtHead(int val) {
        Node node = new Node(val);
        node.next = head;
        if (head != null) head.prev = node;
        head = node;
    }

    public void AddAtTail(int val) {
        Node node = new Node(val);
        if (head == null) {
            head = node;
        } else {
            Node current = head;
            while (current.next != null) {
                current = current.next;
            }
            current.next = node;
            node.prev = current;
        }
    }
    
    public void AddAtIndex(int index, int val) {
        if (index == 0) {
            AddAtHead(val);
            return;
        }
        Node current = head;
        for (int i = 0; i < index - 1 && current != null; i++) {
            current = current.next;
        }
        if (current != null) {
            Node node = new Node(val);
            node.next = current.next;
            if (current.next != null) current.next.prev = node;
            current.next = node;
            node.prev = current;
        }
    }

    public void DeleteAtIndex(int index) {
        Node current = head;
        for (int i = 0; current != null && i < index; i++) {
            current = current.next;
        }
        if (current != null) {
            if (current.prev != null) current.prev.next = current.next;
            else head = current.next;
            if (current.next != null) current.next.prev = current.prev;
        }
    }
}