77 lines
2.1 KiB
Markdown
77 lines
2.1 KiB
Markdown
---
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title: JavaScript Data Structures - Queue
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shortTitle: Queue
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type: story
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language: javascript
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tags: [class]
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author: chalarangelo
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cover: purple-flower-macro-2
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excerpt: A queue is a linear data structure which follows a first in, first out (FIFO) order of operations.
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dateModified: 2021-07-29T05:00:00-04:00
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---
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### Definition
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A queue is a linear data structure that behaves like a real-world queue. It follows a first in, first out (FIFO) order of operations, similar to its real-world counterpart. This means that new items are added to the end of the queue, whereas items are removed from the start of the queue.
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The main operations of a queue data structure are:
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- `enqueue`: Adds an element to the end of the queue
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- `dequeue`: Removes an element from the start of the queue
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- `peek`: Retrieves the element at the start of the queue, without removing it
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- `isEmpty`: Checks if the queue is empty
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### Implementation
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```js
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class Queue {
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constructor() {
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this.items = [];
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}
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enqueue(item) {
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this.items.push(item);
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}
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dequeue(item) {
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return this.items.shift();
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}
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peek(item) {
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return this.items[0];
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}
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isEmpty() {
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return this.items.length === 0;
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}
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}
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```
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- Create a `class` with a `constructor` that initializes an empty array, `items`, for each instance.
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- Define an `enqueue()` method, which uses `Array.prototype.push()` to add an element to the end of the `items` array.
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- Define a `dequeue()` method, which uses `Array.prototype.shift()` to remove an element from the start of the `items` array.
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- Define a `peek()` method, which retrieves the value of the first element in the `items` array, without removing it.
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- Define an `isEmpty()` method, which uses `Array.prototype.length` to determine if the `items` array is empty.
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```js
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const queue = new Queue();
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queue.isEmpty(); // true
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queue.enqueue('A');
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queue.enqueue('B');
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queue.enqueue('C');
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queue.enqueue('D');
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queue.enqueue('E');
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queue.isEmpty(); // false
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queue.peek(); // 'A'
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queue.dequeue(); // 'A'
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queue.dequeue(); // 'B'
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queue.dequeue(); // 'C'
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```
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