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

Practice - 5 Tasks

1fill in blank

easy

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

DSA Typescript

queue.[1](5);

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

Aenqueue

Bpush

Cpop

Ddequeue

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop or dequeue to add elements

Using push which is for stacks, not queues

In a queue, enqueue adds an element to the end.

2fill in blank

medium

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

DSA Typescript

const first = queue.[1]();

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

Apush

Bpeek

Cdequeue

Denqueue

Attempts:

3 left

💡 Hint

Common Mistakes

Using enqueue or push to remove elements

Using peek which only views the first element

dequeue removes and returns the first element in the queue.

3fill in blank

hard

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

DSA Typescript

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

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

Asize

Blength

Ccount

Dempty

Attempts:

3 left

💡 Hint

Common Mistakes

Using size or count which are not valid properties

Using empty which is a method, not a property

The length property gives the number of elements in an array-based queue.

4fill in blank

hard

Fill both blanks to create a queue and add an element to it.

DSA Typescript

const queue = new Array[1]();
queue.[2](10);

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

A<number>

Benqueue

Cpush

D<string>

Attempts:

3 left

💡 Hint

Common Mistakes

Using when numbers are added

Using enqueue which is not an array method

We create a number array with new Array<number>() and add elements using push.

5fill in blank

hard

Fill all three blanks to create a queue, add two elements, and remove one.

DSA Typescript

const queue = new Array[1]();
queue.[2](1);
queue.[3](2);
const first = queue.shift();

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

A<number>

Bpush

D<string>

Attempts:

3 left

💡 Hint

Common Mistakes

Using instead of

Using enqueue which is not an array method

Create a number array, add elements with push, and remove the first with shift.

Practice

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

easy

A. Because queues use less memory than arrays.

B. Because arrays cannot store multiple values.

C. Because a queue follows a specific order (FIFO) which is useful for tasks like scheduling.

D. Because arrays do not allow adding elements.

Solution

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

   A queue follows First-In-First-Out (FIFO) order, meaning the first element added is the first to be removed.

2. Step 2: Compare with arrays and their use cases

   Arrays can store multiple values but do not enforce FIFO order automatically. Queues are designed for tasks like scheduling where order matters.

3. Final Answer:

   Because a queue follows a specific order (FIFO) which is useful for tasks like scheduling. -> Option C

4. Quick Check:

   Queue = FIFO order [OK]

Hint: Queues keep order FIFO, arrays don't enforce order [OK]

Common Mistakes:

• Thinking arrays can't store multiple values
• Confusing memory usage between queues and arrays
• Believing arrays don't allow adding elements

2. Which of the following is the correct way to add an element to the end of a queue in TypeScript?

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 elements at the end of an array

   In TypeScript, push() adds an element to the end of an array, which simulates enqueue in a queue.

2. Step 2: Understand other methods

   pop() removes from the end, shift() removes from the start, and unshift() adds to the start, so they don't add to the end.

3. Final Answer:

   queue.push(element); -> Option A

4. Quick Check:

   push() adds to end [OK]

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

Common Mistakes:

• Using pop() which removes instead of adds
• Using shift() or unshift() incorrectly
• Confusing push() with unshift()

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

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

medium

A. [20, 30]

B. [10, 20, 30]

C. [30, 20]

D. [10, 30]

Solution

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

   Initially empty queue: [] - push(10) -> [10] - push(20) -> [10, 20] - shift() removes first element 10 -> queue becomes [20] - push(30) -> [20, 30]

2. Step 2: Check the final console.log output

   The queue now contains [20, 30], so console.log prints this array.

3. Final Answer:

   [20, 30] -> Option A

4. Quick Check:

   After shift(), queue = [20], then push(30) = [20, 30] [OK]

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

Common Mistakes:

• Thinking shift() removes from end
• Confusing push() and unshift() effects
• Expecting original array unchanged after shift()

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

const queue: number[] = [];
queue.push(1);
queue.push(2);
const removed = queue.pop();
console.log(queue);

medium

A. console.log cannot print arrays.

B. push() cannot add elements to an array.

C. queue is not initialized correctly.

D. Using pop() removes from the end, not the front of the queue.

Solution

1. Step 1: Understand queue removal operation

   In a queue, elements are removed from the front (FIFO). Using pop() removes from the end (LIFO), which is incorrect for a queue.

2. Step 2: Identify the correct method to remove from front

   The correct method to remove from the front is shift(), not pop().

3. Final Answer:

   Using pop() removes from the end, not the front of the queue. -> Option D

4. Quick Check:

   pop() removes end, queue needs front removal [OK]

Hint: Use shift() to remove front, not pop() [OK]

Common Mistakes:

• Thinking pop() removes from front
• Believing push() can't add elements
• Assuming console.log can't print arrays

5. You want to process tasks in the order they arrive and also be able to add urgent tasks that should run before others. Which data structure best solves this problem and why?

hard

A. Queue, because it processes tasks in arrival order only.

B. Priority Queue, because it processes tasks based on priority and arrival order.

C. Array, because it allows random access to tasks.

D. Stack, because it processes the most recent task first.

Solution

1. Step 1: Understand the problem requirements

   Tasks must be processed in arrival order, but urgent tasks should run before others, meaning priority matters.

2. Step 2: Match data structure to requirements

   A normal queue processes strictly FIFO, ignoring priority. A stack processes last-in-first-out, which is not suitable. A priority queue processes tasks based on priority and can maintain arrival order among same priority tasks.

3. Final Answer:

   Priority Queue, because it processes tasks based on priority and arrival order. -> Option B

4. Quick Check:

   Priority Queue = priority + order [OK]

Hint: Use priority queue for priority + order tasks [OK]

Common Mistakes:

• Choosing queue ignoring priority needs
• Confusing stack order with queue order
• Thinking array handles priority automatically