CircularQueue.js

// Circular Queues offer a quick to store FIFO data with a maximum size.
// Conserves memory as we only store up to our capacity
// It is opposed to a queue which could continue to grow if input outpaces output
// Doesn’t use dynamic memory so No memory leaks

class CircularQueue {
 constructor(maxLength) {
 this.queue = []
 this.front = 0
 this.rear = 0
 this.maxLength = maxLength
 }

 // ADD ELEMENTS TO QUEUE
 enqueue(value) {
 if (this.checkOverflow()) return
 if (this.checkEmpty()) {
 this.front += 1
 this.rear += 1
 } else {
 if (this.rear === this.maxLength) {
 this.rear = 1
 } else this.rear += 1
 }
 this.queue[this.rear] = value
 }

 // REMOVES ELEMENTS
 dequeue() {
 if (this.checkEmpty()) {
 // UNDERFLOW
 return
 }
 const y = this.queue[this.front]
 this.queue[this.front] = '*'
 if (!this.checkSingleelement()) {
 if (this.front === this.maxLength) this.front = 1
 else {
 this.front += 1
 }
 }

 return y // Returns the removed element and replaces it with a star
 }

 // checks if the queue is empty or not
 checkEmpty() {
 if (this.front === 0 && this.rear === 0) {
 return true
 }
 }

 checkSingleelement() {
 if (this.front === this.rear && this.rear !== 0) {
 this.front = this.rear = 0
 return true
 }
 }

 // Checks if max capacity of queue has been reached or not
 checkOverflow() {
 if (
 (this.front === 1 && this.rear === this.maxLength) ||
 this.front === this.rear + 1
 ) {
 // CIRCULAR QUEUE OVERFLOW
 return true
 }
 }

 // Prints the entire array ('*' represents blank space)
 display(output = (value) => console.log(value)) {
 for (let index = 1; index < this.queue.length; index++) {
 output(this.queue[index])
 }
 }

 // Displays the length of queue
 length() {
 return this.checkEmpty() ? 0 : this.queue.length - 1
 }

 // Display the top most value of queue
 peek() {
 return this.queue[this.front]
 }
}

export { CircularQueue }