doubly-linked-list.js

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

class DoublyLL {
  #size = 0;
  #head = 0;
  #tail = 0;
  constructor() {
    this.#tail = null;
    this.#size = 0;
    this.#head = null;
  }

  get(index) {
    if (index >= this.#size) throw new Error('Index is out of bound');

    let curr = this.#head
    let count = 0
    while(count < index) {
      curr = curr.next
      count++
    }
    return curr.val
  }

  append(val) {
    this.#size += 1;
    const node = new Node(val);

    if (this.#tail == null) {
      this.#head = node;
      this.#tail = node;
      return;
    }

    node.prev = this.#tail;
    this.#tail.next = node;
    this.#tail = node;
  }

  prepend(val) {
    this.#size += 1;
    const node = new Node(val);

    if (this.#head == null) {
      this.#tail = node;
      this.#head = node;
      return;
    }

    node.next = this.#head;
    this.#head.prev = node;
    this.#head = node;
  }

  insertAt(val, idx) {
    if (idx > this.#size) throw new Error('Index is out of bound');

    let curr = this.#head;
    const node = new Node(val);
    let counter = 1;

    if (idx == 0) {
      this.prepend(val);
      return
    }

    this.#size += 1
    while (curr.next) {
      if (counter == idx) break;
      counter += 1;
      curr = curr.next;
    }
    node.next = curr.next;
    curr.next.prev = node
    curr.next = node;
    node.prev = curr;
  }

  removeHead() {
    this.#head = this.#head.next
    this.#size -= 1
  }
  
  removeTail() {
    this.#tail = this.#tail.prev
    this.#tail.next = null
    this.#size -= 1
  }

  removeAt(index) {
    let count = 1;
    let curr = this.#head;
    
    if(index >= this.#size) throw new Error('Index is out of bound')
    if(index == 0) {
      this.removeHead()
    }

    while (curr.next && count < index) {
      curr = curr.next;
      count++
    }
    curr.next = curr.next.next;
    this.#size-=1
  }

  entries() {
    let res = [];
    let curr = this.#head;
    while (curr.next) {
      res.push(curr.val);
      curr = curr.next;
    }
    res.push(curr.val);
    return res;
  }

  length() {
    return this.#size
  }
}

const dll = new DoublyLL();
dll.append(1);
dll.append(2);
dll.append(3);
dll.append(4);
dll.prepend(5);
dll.insertAt(10, 2);
console.log('after adding: ',dll.entries());
dll.removeHead()
dll.removeTail()
console.log('after remove head, tail: ', dll.entries());
dll.removeAt(2)
console.log('after remove at index 2: ',dll.entries());
console.log('length: ', dll.length());
console.log('val at id 1: ',dll.get(1));