Enqueue Operation in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Javascript

queue.[1](element);

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

Ashift

Benqueue

Cpop

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop which removes the last element instead of adding.

Using shift which removes the first element.

In JavaScript, to add an element at the end of an array (used as a queue), we use push.

2fill in blank

medium

Complete the code to check if the queue is empty before enqueueing.

DSA Javascript

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

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

Acount

Bsize

Clength

Dlength()

Attempts:

3 left

💡 Hint

Common Mistakes

Using size or count which are not valid properties for arrays.

Using length() as a function instead of a property.

The length property gives the number of elements in an array in JavaScript.

3fill in blank

hard

Fix the error in the enqueue function to correctly add an element.

DSA Javascript

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

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

Apop

Bpush

Cshift

Dunshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop which removes the last element.

Using shift which removes the first element.

The push method adds an element to the end of the array, which is the correct enqueue operation.

4fill in blank

hard

Fill both blanks to create a function that enqueues an element and returns the new queue length.

DSA Javascript

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

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

Apush

Bpop

Clength

Dshift

Attempts:

3 left

💡 Hint

Common Mistakes

Returning pop which removes an element instead of length.

Using shift which removes the first element.

The push method adds the element, and length returns the new size of the queue.

5fill in blank

hard

Fill all three blanks to enqueue an element only if the queue size is less than maxSize.

DSA Javascript

function enqueue(queue, element, maxSize) {
  if (queue.[1] < maxSize) {
    queue.[2](element);
    return queue.[3];
  } else {
    return 'Queue full';
  }
}

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

Alength

Bpush

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop which removes elements instead of adding.

Using size or count which are not valid properties.

Check the queue size with length, add element with push, and return the new size with length.

Practice

1. What does the enqueue operation do in a queue data structure?

easy

A. Adds an element to the end of the queue

B. Removes an element from the front of the queue

C. Checks if the queue is empty

D. Returns the size of the queue

Solution

1. Step 1: Understand the queue behavior

   A queue works like a line where new people join at the end.

2. Step 2: Define enqueue operation

   Enqueue means adding a new element at the end of the queue.

3. Final Answer:

   Adds an element to the end of the queue -> Option A

4. Quick Check:

   Enqueue = Add at end [OK]

Hint: Enqueue always adds at the back of the queue [OK]

Common Mistakes:

• Confusing enqueue with dequeue
• Thinking enqueue removes elements
• Mixing enqueue with checking size

2. Which of the following is the correct syntax to add an element 5 to a queue implemented as an array named queue in JavaScript?

easy

A. queue.enqueue(5);

B. queue.add(5);

C. queue.push(5);

D. queue.insert(5);

Solution

1. Step 1: Identify JavaScript array method for adding at end

   JavaScript arrays use push() to add elements at the end.

2. Step 2: Match method to enqueue operation

   Enqueue adds to the end, so queue.push(5); is correct syntax.

3. Final Answer:

   queue.push(5); -> Option C

4. Quick Check:

   Array push adds at end [OK]

Hint: Use push() to enqueue in array-based queue [OK]

Common Mistakes:

• Using non-existent methods like add() or insert()
• Confusing enqueue with dequeue methods
• Trying to use enqueue() directly on array

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

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

medium

A. [10, 20, 30]

B. [30, 20, 10]

C. [10, 30, 20]

D. Error

Solution

1. Step 1: Trace each enqueue operation

   First push adds 10: queue = [10]. Second push adds 20: queue = [10, 20]. Third push adds 30: queue = [10, 20, 30].

2. Step 2: Print the queue array

   Logging queue prints the array as it is: [10, 20, 30].

3. Final Answer:

   [10, 20, 30] -> Option A

4. Quick Check:

   push adds at end, so order is [10, 20, 30] [OK]

Hint: push() adds at end, so order stays as inserted [OK]

Common Mistakes:

• Assuming push adds at front
• Confusing output order
• Expecting error due to empty initialization

4. Identify the error in the following enqueue implementation for a queue using an array:

class Queue {
  constructor() {
    this.items = [];
  }
  enqueue(element) {
    this.items.unshift(element);
  }
}

medium

A. enqueue method should remove element, not add

B. Using unshift adds element at the front, not the end

C. Array should be initialized as null, not []

D. Missing return statement in enqueue method

Solution

1. Step 1: Understand unshift behavior

   unshift adds element at the start (front) of the array, not the end.

2. Step 2: Compare with enqueue operation

   Enqueue must add element at the end, so unshift is incorrect here.

3. Final Answer:

   Using unshift adds element at the front, not the end -> Option B

4. Quick Check:

   Enqueue adds at end, unshift adds at front [OK]

Hint: Use push() for enqueue, not unshift() [OK]

Common Mistakes:

• Confusing unshift with push
• Thinking unshift adds at end
• Ignoring method behavior differences

5. You have a queue implemented with an array. You want to enqueue multiple elements [7, 8, 9] at once while preserving their order. Which code snippet correctly enqueues all elements in order?

hard

A. queue.unshift(7, 8, 9);

B. queue.concat([7, 8, 9]);

C. queue.push([7, 8, 9]);

D. [7, 8, 9].forEach(e => queue.push(e));

Solution

1. Step 1: Analyze each option for enqueue behavior

   queue.push([7, 8, 9]); adds the entire array as one element, not individual elements. queue.concat([7, 8, 9]); creates a new array but does not modify queue. [7, 8, 9].forEach(e => queue.push(e)); pushes each element individually, preserving order. queue.unshift(7, 8, 9); adds elements at front, reversing order.

2. Step 2: Choose the method that enqueues elements individually at the end

   Using forEach with push adds each element in order at the end of queue.

3. Final Answer:

   [7, 8, 9].forEach(e => queue.push(e)); -> Option D

4. Quick Check:

   forEach + push enqueues elements in order [OK]

Hint: Use forEach with push to enqueue multiple elements in order [OK]

Common Mistakes:

• Using push with array adds nested array
• Using unshift reverses order
• Forgetting to assign concat result back to queue