singly_linked_list

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

class LinkedList {
    constructor() {
        this.length = 0;
        this.head = null;
    }

    /**
     * get value of node by index
     * @param {index} number
     * @return {number}
     */
    get(index) {
        if (this.length === 0 || index >= this.length) {
            return -1;
        }
        let node = this.head;
        for (let i = 0; i < index; i++) {
            node = node.next;
        }
        return node.val;
    }

    /**
     * add node at head
     * @param {val} number
     * @return {void}
     */
    addHead(val) {
        let newNode = new Node(val);
        if (this.head === null) {
            this.head = newNode;
        } else {
            newNode.next = this.head;
            this.head = newNode;
        }
        this.length++;
    }

    /**
     * add node at tail
     * @param {val} number
     * @return {void}
     */
    addTail(val) {
        let newNode = new Node(val);
        if (this.length === 0) {
            this.head = newNode;
            this.length++;
            return;
        }
        let node = this.head;
        for (let i = 0; i < this.length - 1; i++) {
            node = node.next;
        }
        node.next = newNode;
        this.length++;
    }

    /**
     * add node by index
     * @param {number} index
     * @param {number} val
     * @return {void}
     */
    addByIndex(index, val) {
        if (index > this.length) {
            return;
        }
        let newNode = new Node(val);
        if (index === 0) {
            newNode.next = this.head;
            this.head = newNode;
            this.length++;
            return;
        }
        let node = this.head;
        for (let i = 0; i < index - 1; i++) {
            node = node.next;
        }
        let prevNode = node;
        let curNode = prevNode.next;
        prevNode.next = newNode;
        newNode.next = curNode;
        this.length++;
    }

    /**
     * delete node by index
     * @param {number} index
     * @return {void}
     */
    deleteByIndex(index) {
        if (index > this.length - 1) {
            return;
        }
        if (index === 0) {
            this.head = this.head.next;
            this.length--;
            return;
        }
        let node = this.head;
        let prevNode = node;
        for (let i = 0; i < index; i++) {
            prevNode = node;
            node = node.next;
        }
        prevNode.next = node.next;
        this.length--;
    }
}

//create linked list
myList = new LinkedList;

//populate linked list
myList.addByIndex(0, 2);
myList.addTail(3);
myList.addHead(1);
myList.addTail(4);
myList.deleteByIndex(3);