Queue.ts

import Node, { DummyHeadNode, DummyTailNode } from './Node';

class Queue<T> {
  private _dummyHead: DummyHeadNode;

  private _dummyTail: DummyTailNode;

  private _length: number;

  constructor() {
    this._dummyHead = new DummyHeadNode();
    this._dummyTail = new DummyTailNode();
    this._dummyHead.next = this._dummyTail;
    this._dummyTail.prev = this._dummyHead;
    this._length = 0;
  }

  /**
   * Adds an element to the back of the Queue.
   * @param {*} element
   * @return {number} The new length of the Queue.
   */
  enqueue(value: T): number {
    const node = new Node(value);
    const prevLast = this._dummyTail.prev as Node<T> | DummyHeadNode;
    prevLast.next = node;

    node.prev = prevLast;
    node.next = this._dummyTail;
    this._dummyTail.prev = node;
    this._length++;
    return this._length;
  }

  /**
   * Removes the element at the front of the Queue.
   * @return {*} The element at the front of the Queue.
   */
  dequeue(): T | undefined {
    if (this.isEmpty()) {
      return undefined;
    }

    const node = this._dummyHead.next as Node<T>;
    const newFirst = node.next as Node<T> | DummyTailNode;
    this._dummyHead.next = newFirst;
    newFirst.prev = this._dummyHead;
    node.next = null;
    this._length--;
    return node.value;
  }

  /**
   * Returns true if the Queue has no elements.
   * @return {boolean} Whether the Queue has no elements.
   */
  isEmpty(): boolean {
    return this._length === 0;
  }

  /**
   * Returns the element at the front of the Queue.
   * @return {*} The element at the front of the Queue.
   */
  front(): T | undefined {
    if (this.isEmpty()) {
      return undefined;
    }

    return (this._dummyHead.next as Node<T>).value;
  }

  /**
   * Returns the element at the back of the Queue.
   * @return {*} The element at the back of the Queue.
   */
  back(): T | undefined {
    if (this.isEmpty()) {
      return undefined;
    }

    return (this._dummyTail.prev as Node<T>).value;
  }

  /**
   * Returns the number of elements in the Queue.
   * @return {number} Number of elements in the Queue.
   */
  get length(): number {
    return this._length;
  }
}

export default Queue;