feat: updated the Queue array to linkedlist DS

Author: fahimfaisaal

Data-Structures/Queue/Queue.js

@@ -1,56 +1,121 @@
 /* Queue
 * A Queue is a data structure that allows you to add an element to the end of
-* a list and remove the item at the front. A queue follows a "First In First Out"
-* system, where the first item to enter the queue is the first to be removed. This
-* implementation uses an array to store the queue.
+* a list and remove the item at the front. A queue follows a FIFO (First In First Out)
+* system, where the first item to enter the queue is the first to be removed,
+* all these operations complexity are O(1).
+* This implementation following the linked list structure.
 */
 
-// Functions: enqueue, dequeue, peek, view, length, empty
 class Queue {
-  // constructor
-  constructor () {
-    // This is the array representation of the queue
-    this.queue = []
+  #size
+
+  constructor (capacity) {
+    if (capacity < 1) {
+      throw new Error('Capacity is not valid')
+    }
+
+    this.head = null
+    this.tail = null
+    this.capacity = capacity
+    this.#size = 0
+
+    return Object.seal(this)
+  }
+
+  get length () {
+    return this.#size
   }
 
-  // methods
-  // Add a value to the end of the queue
-  enqueue (item) {
-    this.queue.push(item)
+  /**
+   * @description - Add a value to the end of the queue
+   * @param {*} data
+   * @returns {number} - The current size of queue
+   */
+  enqueue (data) {
+    if (this.capacity === this.#size) {
+      throw new RangeError('Queue is full')
+    }
+
+    const node = { data, next: null }
+
+    if (!this.head && !this.tail) {
+      this.head = node
+      this.tail = node
+    } else {
+      this.tail.next = node
+      this.tail = node
+    }
+
+    return ++this.#size
   }
 
-  // Removes the value at the front of the queue
+  /**
+   * @description - Removes the value at the front of the queue
+   * @returns {*} - The first data of the queue
+   */
   dequeue () {
-    if (this.empty()) {
+    if (this.isEmpty()) {
       throw new Error('Queue is Empty')
     }
 
-    return this.queue.shift() // remove the item at position 0 from the array and return it
+    const firstData = this.peekFirst()
+
+    this.head = this.head.next
+
+    if (!this.head) {
+      this.tail = null
+    }
+
+    return firstData
   }
 
-  // Return the length of the queue
-  length () {
-    return this.queue.length
+  /**
+   * @description - Return the item at the front of the queue
+   * @returns {*}
+   */
+  peekFirst () {
+    if (this.isEmpty()) {
+      throw new Error('Queue is Empty')
+    }
+
+    return this.head.data
   }
 
-  // Return the item at the front of the queue
-  peek () {
-    if (this.empty()) {
+  /**
+   * @description - Return the item at the tail of the queue
+   * @returns {*}
+   */
+  peekLast () {
+    if (this.isEmpty()) {
       throw new Error('Queue is Empty')
     }
 
-    return this.queue[0]
+    return this.tail.data
   }
 
-  // List all the items in the queue
-  view (output = value => console.log(value)) {
-    output(this.queue)
+  /**
+   * @description - Return the array of Queue
+   * @returns {Array<*>}
+   */
+  toArray () {
+    const array = []
+    let node = this.head
+
+    while (node) {
+      array.push(node.data)
+      node = node.next
+    }
+
+    return array
   }
 
-  // Return Is queue empty ?
-  empty () {
-    return this.queue.length === 0
+  /**
+  * @description - Return is queue empty or not
+  * @returns {boolean}
+  */
+  isEmpty () {
+    return this.length === 0
   }
 }
 
-export { Queue }
+export default Queue

Data-Structures/Queue/test/Queue.test.js

@@ -1,8 +1,17 @@
-import { Queue } from '../Queue'
+import Queue from '../Queue'
+
+describe('Testing the Queue DS', () => {
+  it('Check Capacity', () => {
+    const queue = new Queue(3)
+    queue.enqueue(1)
+    queue.enqueue(2)
+    queue.enqueue(8)
+
+    expect(() => queue.enqueue(9)).toThrow()
+  })
 
-describe('Queue', () => {
   it('Check enqueue/dequeue', () => {
-    const queue = new Queue()
+    const queue = new Queue(10)
     queue.enqueue(1)
     queue.enqueue(2)
     queue.enqueue(8)
@@ -13,36 +22,46 @@ describe('Queue', () => {
   })
 
   it('Check length', () => {
-    const queue = new Queue()
+    const queue = new Queue(5)
 
     queue.enqueue(1)
     queue.enqueue(2)
     queue.enqueue(8)
     queue.enqueue(9)
 
-    expect(queue.length()).toBe(4)
+    expect(queue.toArray()).toEqual([1, 2, 8, 9])
   })
 
-  it('Check peek', () => {
-    const queue = new Queue()
+  it('Check peekFirst & peekLast', () => {
+    const queue = new Queue(4)
 
     queue.enqueue(1)
     queue.enqueue(2)
     queue.enqueue(8)
     queue.enqueue(9)
 
-    expect(queue.peek()).toBe(1)
+    expect(queue.peekFirst()).toBe(1)
+    expect(queue.peekLast()).toBe(9)
   })
 
-  it('Check empty', () => {
+  it('Check toArray', () => {
     const queue = new Queue()
-    expect(queue.empty()).toBeTruthy()
+
+    queue.enqueue(1)
+    queue.enqueue(2)
+    queue.enqueue(8)
+    queue.enqueue(9)
+  })
+
+  it('Check empty', () => {
+    const queue = new Queue(5)
+    expect(queue.isEmpty()).toBeTruthy()
 
     queue.enqueue(1)
     queue.enqueue(2)
     queue.enqueue(8)
     queue.enqueue(9)
 
-    expect(queue.empty()).toBeFalsy()
+    expect(queue.isEmpty()).toBeFalsy()
   })
 })