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export default class Queue {
constructor() {
this._firstNode = null;
this._lastNode = null;
}
/**
* Retrieves the first element in the queue.
* It also removes it from the queue.
* @returns {*}
*/
dequeue() {
if (!this._firstNode) {
return this._firstNode;
}
const payload = this._firstNode.payload;
this._firstNode = this._firstNode.next;
return payload;
}
/**
* Adds an item to the queue
* @param {*} item
*/
enqueue(item) {
const newNode = {
payload: item,
next: null
};
if (this._firstNode === null) {
this._firstNode = newNode;
this._lastNode = newNode;
} else {
this._lastNode.next = newNode;
this._lastNode = newNode;
}
}
/**
* Empties the queue
*/
clear() {
this._firstNode = null;
this._lastNode = null;
}
/**
* Gets the first element of the queue
* @returns {*}
*/
top() {
if (!this._firstNode) {
return this._firstNode;
}
return this._firstNode.payload;
}
/**
* Checks whether the queue is empty or not
* @returns {boolean}
*/
isEmpty() {
return !this._firstNode;
}
}
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