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/* 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 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.

*/

class Queue {

#size

constructor () {

this.head = null

this.tail = null

this.#size = 0

return Object.seal(this)

}

get length () {

return this.#size

}

/**

* @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.isEmpty()) {

throw new Error('Queue is Empty')

}

const firstData = this.peekFirst()

this.head = this.head.next

if (!this.head) {

this.tail = null

}

this.#size--

return firstData

}

/**

* @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

}

/**

* @description - Return the item at the tail of the queue

* @returns {*}

*/

peekLast () {

if (this.isEmpty()) {

throw new Error('Queue is Empty')

}

return this.tail.data

}

/**

* @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

}

/**

* @description - Return is queue empty or not

* @returns {boolean}

*/

isEmpty () {

return this.length === 0

}

}

export default Queue