Description

ES6 implementation of the FIFO queue data structure with TypeScript support.

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Contents

• Description
• Install
• In Depth
• Usage
• Development
• Related
• Team
• License

Install

Yarn

yarn add kiu

NPM

npm install kiu

In Depth

A queue is a linear data structure, or more abstractly a sequential collection, in which the entities are kept in order and the principal operations are the addition of entities to the rear terminal position, known as enqueue, and removal of entities from the front terminal position, known as dequeue. This makes the queue a FIFO, First-In-First-Out, data structure. In this FIFO data structure, the first element added to the queue will be the first one to be removed. Once a new element is added, all elements that were added previously have to be removed before the new one can. Additionally, a peekFirst operation returns the value of the front element without dequeuing it, and a peakLast operation returns the value of the rear element, without mutating the queue as well. Kiu FIFO queues use a linear doubly linked list as their backbone, giving an efficient O(1) performance for the enqueuing and dequeuing operations.

Usage

Kiu exposes a chainable API, that can be utilized through a simple and minimal syntax, allowing you to combine methods effectively.

Usage examples can be also found at the test directory.

'use strict';
const {Queue} = require('kiu');

const queue = new Queue();
//=> Queue { head: null, last: null, length: 0 }

queue.isEmpty();
//=> true

queue.enqueue(10);
//=> Queue {
// head: Item { value: 10, next: null, prev: null },
// last: Item { value: 10, next: null, prev: null },
// length: 1 }

queue.isEmpty();
//=> false

queue.peekFirst();
//=> 10

queue
  .enqueue(20)
  .enqueue(30)
  .enqueue(40)
  .enqueue(50);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 50, next: null, prev:
//   Item { value: 40, next: [Circular], prev: [Item] } },
// length: 5 }

queue.includes(30);
//=> true

queue.includes(60);
//=> false

queue.dequeue();
//=> 10

queue.peekFirst();
//=> 20

queue.peekLast();
//=> 50

queue.toArray();
//=> [ 20, 30, 40, 50 ]

queue.rotateRight(1);
//=> Queue {
// head:
//   Item { value: 30, prev: null, next:
//   Item { value: 40, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 20, next: null, prev:
//   Item { value: 50, next: [Circular], prev: [Item] } },
// length: 4 }

queue.toArray();
//=> [ 30, 40, 50, 20 ]

queue.rotateLeft(3);
//=> Queue {
// head:
//   Item { value: 40, prev: null, next:
//   Item { value: 50, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 30, next: null, prev:
//   Item { value: 20, next: [Circular], prev: [Item] } },
// length: 4 }

queue.toArray();
//=> [ 40, 50, 20, 30 ]

queue
  .reverse()
  .map(x => x * 10)
  .toArray();
//=> [ 300, 200, 500, 400 ]

queue.nth(2);
//=> 500

API

queue.length

• Return Type: Number

Returns the total number of values in the queue.

const {Queue} = require('kiu');

const queue = new Queue();

queue
  .enqueue(10)
  .enqueue(20);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: null } },
// last:
//   Item { value: 20, next: null, prev:
//   Item { value: 10, next: [Circular], prev: null } },
// length: 2 }
queue.length;
//=> 2

queue.clear()

• Return Type: Queue

Mutates the queue by removing all residing values and returns it empty.

const {Queue} = require('kiu');

const queue = new Queue();

queue
  .enqueue(10)
  .enqueue(20)
  .enqueue(30);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 30, next: null, prev:
//   Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.length;
//=> 3
queue.clear();
//=> Queue { head: null, last: null, length: 0 }
queue.length;
//=> 0

queue.dequeue()

• Return Type: Any | undefined

Mutates the queue by removing the value located at the front terminal position. Returns the removed value, if the queue is not empty, or undefined if it is.

const {Queue} = require('kiu');

const queue = new Queue();

queue.enqueue(10);
//=> Queue {
// head: Item { value: 10, prev: null, next: null }
// last: Item { value: 10, prev: null, next: null }
// length: 1 }
queue.dequeue();
//=> 10
queue.dequeue();
//=> undefined

queue.enqueue(value)

• Return Type: Queue

Mutates the queue by inserting a new value at the rear terminal position. Returns the queue itself.

value

• Type: Any

Value to insert.

const {Queue} = require('kiu');

const queue = new Queue();

queue.enqueue(10);
//=> Queue {
// head: Item { value: 10, prev: null, next: null }
// last: Item { value: 10, prev: null, next: null }
// length: 1 }
queue.enqueue(20).enqueue(30);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 30, next: null, prev:
//   Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.length;
//=> 3

queue.forEach(fn)

• Return Type: Queue

Traverses the queue, from the front to the rear, and executes the provided fn function once for each traversed value, without mutating the queue. Returns the queue itself at the end of the traversal.

fn

• Type: Function

Unary function to execute for each traversed value.

const {Queue} = require('kiu');

const queue = new Queue();

queue
  .enqueue(10)
  .enqueue(20)
  .enqueue(30);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 30, next: null, prev:
//   Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.forEach(console.log);
//=> 10
// 20
// 20

queue.includes(value)

• Return Type: Boolean

Determines whether the queue includes a certain value, returning true or false as appropriate.

value

• Type: Any

Value to search for.

const {Queue} = require('kiu');

const queue = new Queue();

queue
  .enqueue(10)
  .enqueue(20)
  .enqueue(30);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 30, next: null, prev:
//   Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.includes(10);
//=> true
queue.includes(40);
//=> false
queue.includes(20);
//=> true

queue.isEmpty()

• Return Type: Boolean

Determines whether the queue is empty, returning true or false as appropriate.

const {Queue} = require('kiu');

const queue = new Queue();

queue.isEmpty();
//=> true
queue.enqueue(10);
//=> Queue {
// head: Item { value: 10, prev: null, next: null }
// last: Item { value: 10, prev: null, next: null }
// length: 1 }
queue.isEmpty();
//=> false

queue.map(fn)

• Return Type: Queue

Traverses the queue, from front to rear, and mutates it by updating each stored value with the result of calling once the provided fn function on it. Returns the in-place mutated queue at the end of the traversal.

fn

• Type: Function

Unary function that produces a value of the mutated queue.

const {Queue} = require('kiu');

const queue = new Queue();

queue
  .enqueue(10)
  .enqueue(20)
  .enqueue(30);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 30, next: null, prev:
//   Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.map(x => x * 10);
//=> Queue {
// head:
//   Item { value: 100, prev: null, next:
//   Item { value: 200, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 300, next: null, prev:
//   Item { value: 200, next: [Circular], prev: [Item] } },
// length: 3 }

queue.nth(n)

• Return Type: Any | undefined

Traverses the queue, from front to rear, and returns the nth value. If the value does not exist, then undefined is returned. The queue values follow zero-based numbering, thus the first/initial value corresponds to index 0.

n

• Type: Number

Zero-based queue index number.

const {Queue} = require('kiu');

const queue = new Queue();

queue
  .enqueue(10)
  .enqueue(20)
  .enqueue(30);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 30, next: null, prev:
//   Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.nth(0);
//=> 10
queue.nth(2);
//=> 30
queue.nth(3);
//=> undefined

queue.peekFirst()

• Return Type: Any | undefined

Returns the first value, located at the front of the queue, without mutating the queue itself. If the queue is empty, then undefined is returned.

const {Queue} = require('kiu');

const queue = new Queue();

queue
  .enqueue(10)
  .enqueue(20)
  .enqueue(30);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 30, next: null, prev:
//   Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.peekFirst();
//=> 10

queue.peekLast()

• Return Type: Any | undefined

Returns the last value, located at the rear of the queue, without mutating the queue itself. If the queue is empty, then undefined is returned.

const {Queue} = require('kiu');

const queue = new Queue();

queue
  .enqueue(10)
  .enqueue(20)
  .enqueue(30);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 30, next: null, prev:
//   Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.peekLast();
//=> 30

queue.reverse()

• Return Type: Queue

Mutates the queue by reversing in-place the residing values. The first value becomes the last one, and the last one becomes the first. Returns the reversed queue.

const {Queue} = require('kiu');

const queue = new Queue();

queue
  .enqueue(10)
  .enqueue(20)
  .enqueue(30);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 30, next: null, prev:
//   Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.toArray();
//=> [ 10, 20, 30 ]
queue.reverse();
//=> Queue {
// head:
//   Item { value: 30, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 10, next: null, prev:
//   Item { value: 20, next: [Circular], prev: [Item] } },
// length: 3 }
queue.toArray();
//=> [ 30, 20, 10 ]

queue.rotateLeft(n)

• Return Type: Queue

Mutates the queue by moving the n rear-most values to the front of the queue in a rotating fashion. Returns the queue itself.

n

• Type: Number

Number of rear-most values to be rotated.

const {Queue} = require('kiu');

const queue = new Queue();

queue
  .enqueue(10)
  .enqueue(20)
  .enqueue(30)
  .enqueue(40)
  .enqueue(50);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 50, next: null, prev:
//   Item { value: 40, next: [Circular], prev: [Item] } },
// length: 5 }
queue.toArray();
//=> [ 10, 20, 30, 40, 50 ]
queue.rotateLeft(2);
//=> Queue {
// head:
//   Item { value: 40, prev: null, next:
//   Item { value: 50, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 30, next: null, prev:
//   Item { value: 20, next: [Circular], prev: [Item] } },
// length: 5 }
queue.toArray();
//=> [ 40, 50, 10, 20, 30 ]

queue.rotateRight(n)

• Return Type: Queue

Mutates the queue by moving the n front-most items to the rear of the queue in a rotating fashion. Returns the queue itself.

n

• Type: Number

Number of front-most values to be rotated.

const {Queue} = require('kiu');

const queue = new Queue();

queue
  .enqueue(10)
  .enqueue(20)
  .enqueue(30)
  .enqueue(40)
  .enqueue(50);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 50, next: null, prev:
//   Item { value: 40, next: [Circular], prev: [Item] } },
// length: 5 }
queue.toArray();
//=> [ 10, 20, 30, 40, 50 ]
queue.rotateRight(2);
//=> Queue {
// head:
//   Item { value: 30, prev: null, next:
//   Item { value: 40, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 20, next: null, prev:
//   Item { value: 10, next: [Circular], prev: [Item] } },
// length: 5 }
queue.toArray();
//=> [ 30, 40, 50, 10, 20 ]

queue.toArray()

• Return Type: Array<Any>

The method traverses the queue, from front to rear, and stores each traversed value in an array. The array is returned at the end of the traversal.

const {Queue} = require('kiu');

const queue = new Queue();

queue
  .enqueue(10)
  .enqueue(20)
  .enqueue(30)
  .enqueue(40)
  .enqueue(50);
//=> Queue {
// head:
//   Item { value: 10, prev: null, next:
//   Item { value: 20, prev: [Circular], next: [Item] } },
// last:
//   Item { value: 50, next: null, prev:
//   Item { value: 40, next: [Circular], prev: [Item] } },
// length: 5 }
queue.toArray();
//=> [ 10, 20, 30, 40, 50 ]

Development

For more info on how to contribute to the project, please read the contributing guidelines.

• Fork the repository and clone it to your machine
• Navigate to your local fork: cd kiu
• Install the project dependencies: npm install or yarn install
• Lint the code and run the tests: npm test or yarn test

Related

• avlbinstree - AVL self-balancing binary search trees for ES6
• binstree - Binary search trees for ES6
• doublie - Doubly circular & linear linked lists for ES6
• mheap - Binary min & max heaps for ES6
• prioqueue - Priority queues for ES6
• shtack - LIFO Stacks for ES6
• singlie - Singly circular & linear linked lists for ES6

Team

• Klaus Sinani (@klaussinani)

License

MIT