merge: Improved the complexity of dequeue O(n) to O(1) (TheAlgorithms#1005)

fahimfaisaal · web-flow · commit e05b4432d86a · 2022-05-06T21:50:55.000+05:30
* feat: improved memoize function used Map instead of object & used the JSON.stringfy method for generate a valid string as a key * docs: modified documentation * style: format with standard * docs: modified stringify doc * refactor: remove two repetition implementation * feat: added validation, test codes * chore: remove useless words * feat: added types for jest * chore: added link box * feat: added new validation test casses & methods * style: formated with standard * feat: added parse method & test cases * docs: added js docs * chore: added default import export * feat: imporved algorithm via replace method * test: added two test cases * feat: added jest type for suggestions * feat: added `reduceRight` & `trim` method * chore: added helper variable * feat: added new rotation option * Revert "chore: added helper variable" This reverts commit 489544d. * remove: yarn lock * chore: fix grammer * feat: used replace method & added test case * feat: remove revert * chore: added new line * feat: updated the Queue array to linkedlist DS * chore: fixed grammer * resolve: removed capacity related codes, & updated test cases * feat: added length dicrease code on dequeue
diff --git a/Data-Structures/Queue/Queue.js b/Data-Structures/Queue/Queue.js
@@ -1,56 +1,114 @@
 /* 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 operation complexities are O(1).
+* This implementation following the linked list structure.
 */
 
-// Functions: enqueue, dequeue, peek, view, length, empty
 class Queue {
-  // constructor
+  #size
+
   constructor () {
-    // This is the array representation of the queue
-    this.queue = []
+    this.head = null
+    this.tail = null
+    this.#size = 0
+
+    return Object.seal(this)
   }
 
-  // methods
-  // Add a value to the end of the queue
-  enqueue (item) {
-    this.queue.push(item)
+  get length () {
+    return this.#size
   }
 
-  // Removes the value at the front of the queue
+  /**
+   * @description - Add a value to the end of the queue
+   * @param {*} data
+   * @returns {number} - The current size of queue
+   */
+  enqueue (data) {
+    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
+  }
+
+  /**
+   * @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
+    }
+
+    this.#size--
+
+    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
diff --git a/Data-Structures/Queue/test/Queue.test.js b/Data-Structures/Queue/test/Queue.test.js
@@ -1,48 +1,46 @@
-import { Queue } from '../Queue'
+import Queue from '../Queue'
 
-describe('Queue', () => {
-  it('Check enqueue/dequeue', () => {
-    const queue = new Queue()
-    queue.enqueue(1)
-    queue.enqueue(2)
-    queue.enqueue(8)
-    queue.enqueue(9)
+describe('Testing the Queue DS', () => {
+  const queue = new Queue()
 
-    expect(queue.dequeue()).toBe(1)
-    expect(queue.dequeue()).toBe(2)
+  it('Testing enqueue method', () => {
+    expect(queue.enqueue(1)).toBe(1)
+    expect(queue.enqueue(2)).toBe(2)
+    expect(queue.enqueue(8)).toBe(3)
+    expect(queue.enqueue(9)).toBe(4)
   })
 
-  it('Check length', () => {
-    const queue = new Queue()
-
-    queue.enqueue(1)
-    queue.enqueue(2)
-    queue.enqueue(8)
-    queue.enqueue(9)
+  it('Testing length after enqueue', () => {
+    expect(queue.length).toBe(4)
+  })
 
-    expect(queue.length()).toBe(4)
+  it('Testing peekFirst & peekLast methods', () => {
+    expect(queue.peekFirst()).toBe(1)
+    expect(queue.peekLast()).toBe(9)
   })
 
-  it('Check peek', () => {
-    const queue = new Queue()
+  it('Testing toArray method', () => {
+    expect(queue.toArray()).toEqual([1, 2, 8, 9])
+  })
 
-    queue.enqueue(1)
-    queue.enqueue(2)
-    queue.enqueue(8)
-    queue.enqueue(9)
+  it('Testing dequeue method', () => {
+    expect(queue.dequeue()).toBe(1)
+    expect(queue.dequeue()).toBe(2)
+  })
 
-    expect(queue.peek()).toBe(1)
+  it('Testing length after dequeue', () => {
+    expect(queue.length).toBe(2)
   })
 
-  it('Check empty', () => {
+  it('Testing isEmpty method', () => {
     const queue = new Queue()
-    expect(queue.empty()).toBeTruthy()
+    expect(queue.isEmpty()).toBeTruthy()
 
     queue.enqueue(1)
     queue.enqueue(2)
     queue.enqueue(8)
     queue.enqueue(9)
 
-    expect(queue.empty()).toBeFalsy()
+    expect(queue.isEmpty()).toBeFalsy()
   })
 })
