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Implement a Queue

curriculum/challenges/english/blocks/lab-implement-a-queue/69aaafeaa4037197c75587cd.md

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--description--

In this lab, you will implement a queue data structure using functions. A queue is a First-In-First-Out (FIFO) data structure where elements are added to the back of the queue and removed from the front.

Objective: Fulfill the user stories below and get all the tests to pass to complete the lab.

User Stories:

  1. You should have a enqueue function that adds an element to the back of the queue.
  2. You should have a dequeue function that removes and returns the front element of the queue.
  3. You should have a front function that returns the front element of the queue without removing it.
  4. You should have a size function that returns the number of elements in the queue.
  5. You should have an isEmpty function that returns true if the queue is empty and false otherwise.

--hints--

You should have an enqueue function.

js
assert.isFunction(enqueue);

enqueue function should add an element to the back of the queue.

js
const queue = initQueue();
enqueue(queue, 'first');
enqueue(queue, 'second');
assert.strictEqual(front(queue), 'first');
assert.strictEqual(size(queue), 2);

You should have a dequeue function.

js
assert.isFunction(dequeue);

dequeue function should remove and return the front element of the queue.

js
const queue = initQueue();
enqueue(queue, 'first');
enqueue(queue, 'second');
enqueue(queue, 'third');
assert.strictEqual(dequeue(queue), 'first');
assert.strictEqual(dequeue(queue), 'second');
assert.strictEqual(size(queue), 1);

dequeue should return undefined when called on an empty queue.

js
const queue = initQueue();
assert.isUndefined(dequeue(queue));

enqueue should continue to add elements to the back of the queue after dequeues.

js
const queue = initQueue();
enqueue(queue, 'first');
enqueue(queue, 'second');
assert.strictEqual(dequeue(queue), 'first');
enqueue(queue, 'third');
assert.strictEqual(front(queue), 'second');
assert.strictEqual(dequeue(queue), 'second');
assert.strictEqual(dequeue(queue), 'third');

Different queue instances should not share state.

js
const queueOne = initQueue();
const queueTwo = initQueue();
enqueue(queueOne, 'first');
enqueue(queueTwo, 'second');
assert.strictEqual(front(queueOne), 'first');
assert.strictEqual(front(queueTwo), 'second');
assert.strictEqual(size(queueOne), 1);
assert.strictEqual(size(queueTwo), 1);

You should have a front function.

js
assert.isFunction(front);

front function should return the front element of the queue without removing it.

js
const queue = initQueue();
enqueue(queue, 'first');
enqueue(queue, 'second');
assert.strictEqual(front(queue), 'first');
assert.strictEqual(front(queue), 'first');
assert.strictEqual(size(queue), 2);

front should return undefined when called on an empty queue.

js
const queue = initQueue();
assert.isUndefined(front(queue));

You should have a size function.

js
assert.isFunction(size);

size function should return the correct number of elements in the queue.

js
const queue = initQueue();
assert.strictEqual(size(queue), 0);
enqueue(queue, 'first');
assert.strictEqual(size(queue), 1);
enqueue(queue, 'second');
enqueue(queue, 'third');
assert.strictEqual(size(queue), 3);
dequeue(queue);
assert.strictEqual(size(queue), 2);

You should have an isEmpty function.

js
assert.isFunction(isEmpty);

isEmpty function should return true for an empty queue.

js
const queue = initQueue();
assert.isTrue(isEmpty(queue));

isEmpty function should return false for a non-empty queue.

js
const queue = initQueue();
enqueue(queue, 'element');
assert.isFalse(isEmpty(queue));

isEmpty function should return true after all elements are removed from the queue.

js
const queue = initQueue();
enqueue(queue, 'first');
enqueue(queue, 'second');
dequeue(queue);
dequeue(queue);
assert.isTrue(isEmpty(queue));

--seed--

--seed-contents--

js
function initQueue() {
  return {
    collection: []
  };
}

function print(queue) {
  console.log(queue.collection);
}

function enqueue(queue, element) {
  
}

function dequeue(queue) {
  
}

function front(queue) {
  
}

function size(queue) {
  
}

function isEmpty(queue) {
  
}

--solutions--

js
function initQueue() {
  return {
    collection: []
  };
}

function print(queue) {
  console.log(queue.collection);
}

function enqueue(queue, element) {
  queue.collection.push(element);
}

function dequeue(queue) {
  return queue.collection.shift();
}

function front(queue) {
  return queue.collection[0];
}

function size(queue) {
  return queue.collection.length;
}

function isEmpty(queue) {
  return queue.collection.length === 0;
}