Solution.ts

class LinkNode {
    public val: number;
    public next: LinkNode;

    constructor(val: number, next: LinkNode = null) {
        this.val = val;
        this.next = next;
    }
}

class MyLinkedList {
    public head: LinkNode;

    constructor() {
        this.head = null;
    }

    get(index: number): number {
        if (this.head == null) {
            return -1;
        }
        let cur = this.head;
        let idxCur = 0;
        while (idxCur < index) {
            if (cur.next == null) {
                return -1;
            }
            cur = cur.next;
            idxCur++;
        }
        return cur.val;
    }

    addAtHead(val: number): void {
        this.head = new LinkNode(val, this.head);
    }

    addAtTail(val: number): void {
        const newNode = new LinkNode(val);
        if (this.head == null) {
            this.head = newNode;
            return;
        }
        let cur = this.head;
        while (cur.next != null) {
            cur = cur.next;
        }
        cur.next = newNode;
    }

    addAtIndex(index: number, val: number): void {
        if (index <= 0) {
            return this.addAtHead(val);
        }
        const dummy = new LinkNode(0, this.head);
        let cur = dummy;
        let idxCur = 0;
        while (idxCur < index) {
            if (cur.next == null) {
                return;
            }
            cur = cur.next;
            idxCur++;
        }
        cur.next = new LinkNode(val, cur.next || null);
    }

    deleteAtIndex(index: number): void {
        if (index == 0) {
            this.head = (this.head || {}).next;
            return;
        }
        const dummy = new LinkNode(0, this.head);
        let cur = dummy;
        let idxCur = 0;
        while (idxCur < index) {
            if (cur.next == null) {
                return;
            }
            cur = cur.next;
            idxCur++;
        }
        cur.next = (cur.next || {}).next;
    }
}

/**
 * Your MyLinkedList object will be instantiated and called as such:
 * var obj = new MyLinkedList()
 * var param_1 = obj.get(index)
 * obj.addAtHead(val)
 * obj.addAtTail(val)
 * obj.addAtIndex(index,val)
 * obj.deleteAtIndex(index)
 */