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ArrayQueue.js
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Created: Mon, Jun 16, 00:04

ArrayQueue.js
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	/*
	MIT License http://www.opensource.org/licenses/mit-license.php
	Author Tobias Koppers @sokra
	*/

	"use strict";

	/**
	* @template T
	*/
	class ArrayQueue {
	/**
	* @param {Iterable<T>=} items The initial elements.
	*/
	constructor(items) {
	/** @private @type {T[]} */
	this._list = items ? Array.from(items) : [];
	/** @private @type {T[]} */
	this._listReversed = [];
	}

	/**
	* Returns the number of elements in this queue.
	* @returns {number} The number of elements in this queue.
	*/
	get length() {
	return this._list.length + this._listReversed.length;
	}

	/**
	* Empties the queue.
	*/
	clear() {
	this._list.length = 0;
	this._listReversed.length = 0;
	}

	/**
	* Appends the specified element to this queue.
	* @param {T} item The element to add.
	* @returns {void}
	*/
	enqueue(item) {
	this._list.push(item);
	}

	/**
	* Retrieves and removes the head of this queue.
	* @returns {T \| undefined} The head of the queue of `undefined` if this queue is empty.
	*/
	dequeue() {
	if (this._listReversed.length === 0) {
	if (this._list.length === 0) return undefined;
	if (this._list.length === 1) return this._list.pop();
	if (this._list.length < 16) return this._list.shift();
	const temp = this._listReversed;
	this._listReversed = this._list;
	this._listReversed.reverse();
	this._list = temp;
	}
	return this._listReversed.pop();
	}

	/**
	* Finds and removes an item
	* @param {T} item the item
	* @returns {void}
	*/
	delete(item) {
	const i = this._list.indexOf(item);
	if (i >= 0) {
	this._list.splice(i, 1);
	} else {
	const i = this._listReversed.indexOf(item);
	if (i >= 0) this._listReversed.splice(i, 1);
	}
	}

	[Symbol.iterator]() {
	let i = -1;
	let reversed = false;
	return {
	next: () => {
	if (!reversed) {
	i++;
	if (i < this._list.length) {
	return {
	done: false,
	value: this._list[i]
	};
	}
	reversed = true;
	i = this._listReversed.length;
	}
	i--;
	if (i < 0) {
	return {
	done: true,
	value: undefined
	};
	}
	return {
	done: false,
	value: this._listReversed[i]
	};
	}
	};
	}
	}

	module.exports = ArrayQueue;

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