Why Queue Exists and What Problems It Solves in DSA Javascript - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add an element to the end of the queue.

DSA Javascript

queue.push([1]);

Drag options to blanks, or click blank then click option'

Aelement

Bpop()

Cshift()

Dunshift()

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() which removes from the end instead of adding.

Using shift() or unshift() which affect the start of the array.

To add an element to the end of a queue, we use push() with the element as argument.

2fill in blank

medium

Complete the code to remove the first element from the queue.

DSA Javascript

const removed = queue.[1]();

Drag options to blanks, or click blank then click option'

Ashift

Bpop

Cpush

Dunshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() which removes from the end.

Using push() or unshift() which add elements instead of removing.

To remove the first element from a queue, use shift() which removes from the front.

3fill in blank

hard

Fix the error in the code to correctly check if the queue is empty.

DSA Javascript

if (queue.[1] === 0) {
  console.log('Queue is empty');
}

Drag options to blanks, or click blank then click option'

Asize

Bcount

Clength

Dempty

Attempts:

3 left

💡 Hint

Common Mistakes

Using non-existent properties like size or count.

Trying to call a method instead of accessing a property.

Arrays in JavaScript use length to check how many elements they have.

4fill in blank

hard

Fill both blanks to create a function that enqueues and dequeues elements correctly.

DSA Javascript

function processQueue(queue, element) {
  queue.[1](element);
  return queue.[2]();
}

Drag options to blanks, or click blank then click option'

Apush

Bshift

Cpop

Dunshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() to remove the first element instead of shift().

Using unshift() which adds to the front instead of push().

To add an element, use push. To remove the first element, use shift.

5fill in blank

hard

Fill all three blanks to create a function that returns the queue length after enqueue and dequeue operations.

DSA Javascript

function updateQueue(queue, element) {
  queue.[1](element);
  queue.[2]();
  return queue.[3];
}

Drag options to blanks, or click blank then click option'

Apush

Bshift

Clength

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() instead of shift() to remove the first element.

Trying to call length as a function instead of property.

Use push to add, shift to remove the first element, and length to get the current size.

Practice

1. Why do we use a Queue data structure instead of just using an array for all tasks?

easy

A. Because arrays cannot store multiple elements.

B. Because a queue follows a strict order of processing elements, first in first out (FIFO).

C. Because queues allow random access to elements anywhere in the list.

D. Because queues use less memory than arrays.

Solution

1. Step 1: Understand the order of processing in a queue

   A queue processes elements in the order they arrive, which is called FIFO (first in, first out).

2. Step 2: Compare with arrays

   Arrays allow access to any element randomly, but queues restrict access to only the front and back, enforcing order.

3. Final Answer:

   Because a queue follows a strict order of processing elements, first in first out (FIFO). -> Option B

4. Quick Check:

   Queue = FIFO order [OK]

Hint: Queues process items in order, arrays do not enforce order [OK]

Common Mistakes:

• Thinking arrays cannot store multiple elements
• Believing queues allow random access
• Confusing memory usage between arrays and queues

2. Which of the following is the correct way to add an element to the end of a queue implemented as an array in JavaScript?

easy

A. queue.push(element)

B. queue.pop(element)

C. queue.shift(element)

D. queue.unshift(element)

Solution

1. Step 1: Identify the method to add at the end of an array

   In JavaScript, push() adds an element to the end of an array.

2. Step 2: Confirm queue behavior

   Since a queue adds elements at the back, push() is the correct method.

3. Final Answer:

   queue.push(element) -> Option A

4. Quick Check:

   Adding to queue end = push() [OK]

Hint: Use push() to add at queue's end in JavaScript [OK]

Common Mistakes:

• Using pop() which removes from end
• Using shift() which removes from front
• Using unshift() which adds to front

3. What will be the output of the following JavaScript code simulating a queue?

const queue = [];
queue.push(10);
queue.push(20);
queue.push(30);
const first = queue.shift();
queue.push(40);
console.log(queue);

medium

A. [30, 40]

B. [10, 20, 30, 40]

C. [20, 30, 40]

D. [40, 10, 20, 30]

Solution

1. Step 1: Trace queue operations step-by-step

   Initially queue = []. After push(10), queue = [10]. After push(20), queue = [10, 20]. After push(30), queue = [10, 20, 30].

2. Step 2: Remove first element and add new element

   shift() removes 10, so queue = [20, 30]. Then push(40) adds 40 at end, queue = [20, 30, 40].

3. Final Answer:

   [20, 30, 40] -> Option C

4. Quick Check:

   shift removes front, push adds end [OK]

Hint: shift() removes front, push() adds end [OK]

Common Mistakes:

• Forgetting shift() removes first element
• Assuming push adds at front
• Confusing array output order

4. The following code is intended to simulate a queue but has a bug. What is the bug?

const queue = [];
queue.unshift(1);
queue.unshift(2);
queue.pop();
console.log(queue);

medium

A. Using unshift to add elements adds them to the front, reversing order.

B. pop() removes from the front instead of the end.

C. The queue is empty after these operations.

D. The queue should use push() and shift() for correct FIFO behavior.

Solution

1. Step 1: Analyze the methods used

   unshift() adds elements to the front, pop() removes from the end. This reverses the order and breaks FIFO.

2. Step 2: Identify correct queue methods

   For FIFO, add at end with push(), remove from front with shift().

3. Final Answer:

   The queue should use push() and shift() for correct FIFO behavior. -> Option D

4. Quick Check:

   Queue FIFO = push() + shift() [OK]

Hint: Queue add = push(), remove = shift() for FIFO [OK]

Common Mistakes:

• Using unshift() to add elements
• Using pop() to remove front element
• Assuming pop() removes front element

5. You need to process tasks in the exact order they arrive but also want to peek at the next task without removing it. Which queue operation combination solves this best?

hard

A. Use push() to add, shift() to remove, and access queue[0] to peek.

B. Use unshift() to add, pop() to remove, and access queue[queue.length-1] to peek.

C. Use push() to add, pop() to remove, and access queue[queue.length-1] to peek.

D. Use unshift() to add, shift() to remove, and access queue[0] to peek.

Solution

1. Step 1: Understand queue order and operations

   Queue adds at end (push), removes from front (shift) to keep FIFO order.

2. Step 2: Identify how to peek without removing

   Peeking means looking at the front element without removing it, which is queue[0].

3. Final Answer:

   Use push() to add, shift() to remove, and access queue[0] to peek. -> Option A

4. Quick Check:

   Peek front = queue[0], add = push(), remove = shift() [OK]

Hint: Peek front with queue[0], add with push(), remove with shift() [OK]

Common Mistakes:

• Using pop() to remove front element
• Using unshift() to add elements
• Peeking at wrong index