Queue Concept and FIFO Principle in DSA Typescript - Interactive Practice

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

Cinsert

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'enqueue' which is not a built-in array method in TypeScript.

In TypeScript arrays used as queues, push adds an element to the end, following FIFO.

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'

Ashift

Bpop

Cdequeue

Dremove

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pop' which removes the last element, not the first.

The shift method removes the first element from an array, which matches FIFO removal in a queue.

3fill in blank

hard

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

DSA Typescript

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

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

Alength

Bsize

Clength()

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'length()' as if it were a function.

The length property gives the number of elements in an array. It is not a function, so no parentheses.

4fill in blank

hard

Fill both blanks to create a queue from an array and remove the first element.

DSA Typescript

const queue = [1];
const removed = queue.[2]();

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

A[1, 2, 3, 4]

Bpop

Cshift

D[]

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pop' which removes the last element instead of the first.

We create a queue as an array [1, 2, 3, 4] and remove the first element using shift().

5fill in blank

hard

Fill all three blanks to add an element, remove the first, and check if the queue is empty.

DSA Typescript

queue.[1](10);
const first = queue.[2]();
if (queue.[3] === 0) {
  console.log('Empty now');
}

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

Apush

Bshift

Clength

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pop' to remove the first element.

We add with push, remove with shift, and check emptiness with length.

Practice

1. What does the FIFO principle mean in the context of a queue?

easy

A. First In, First Out - the first element added is the first removed

B. First In, First Out - the last element added is the first removed

C. Last In, First Out - the first element added is the last removed

D. Last In, First Out - the last element added is the last removed

Solution

1. Step 1: Understand FIFO meaning

   FIFO means the first element that enters the queue is the first to leave.

2. Step 2: Match FIFO to queue behavior

   Queues follow FIFO, so the first added element is removed first.

3. Final Answer:

   First In, First Out - the first element added is the first removed -> Option A

4. Quick Check:

   FIFO = First In, First Out [OK]

Hint: Remember queue = line; first come, first served [OK]

Common Mistakes:

• Confusing FIFO with LIFO
• Thinking last added is removed first
• Mixing queue with stack behavior

2. Which of the following is the correct TypeScript syntax to create an empty queue using an array?

easy

A. let queue = {};

B. const queue: number[] = [];

C. const queue = new Queue();

D. queue = [];

Solution

1. Step 1: Identify TypeScript array syntax

   To create an empty array of numbers, use const queue: number[] = [];

2. Step 2: Check other options

   const queue = new Queue(); uses a class not defined here, A creates an object, D is missing declaration keyword.

3. Final Answer:

   const queue: number[] = []; -> Option B

4. Quick Check:

   Array declaration with type and empty brackets [OK]

Hint: Use const with type and empty brackets for empty array [OK]

Common Mistakes:

• Using object {} instead of array []
• Missing type annotation in TypeScript
• Omitting declaration keyword (const/let)

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

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

medium

A. []

B. [10, 20, 30]

C. [30]

D. [20, 30]

Solution

1. Step 1: Add elements to queue

   Elements 10, 20, 30 are added to the queue in order.

2. Step 2: Remove first element using shift()

   shift() removes 10, so queue now contains [20, 30].

3. Final Answer:

   [20, 30] -> Option D

4. Quick Check:

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

Hint: shift() removes first element, push() adds last [OK]

Common Mistakes:

• Confusing shift() with pop()
• Expecting original array unchanged
• Thinking push() removes elements

4. Identify the error in this TypeScript queue code:

const queue: number[] = [];
queue.push(5);
queue.push(10);
const removed = queue.pop();
console.log(queue);

medium

A. Using pop() removes last, not first element in queue

B. push() is not valid for arrays

C. queue should be declared as object, not array

D. Missing type annotation for queue

Solution

1. Step 1: Understand queue removal method

   Queue removes elements in FIFO order, so first element should be removed.

2. Step 2: Check method used

   pop() removes last element, which breaks FIFO principle.

3. Final Answer:

   Using pop() removes last, not first element in queue -> Option A

4. Quick Check:

   Queue removal must use shift(), not pop() [OK]

Hint: Use shift() to remove first, pop() removes last [OK]

Common Mistakes:

• Using pop() instead of shift() for queue
• Thinking push() removes elements
• Confusing array with object declaration

5. You have a queue implemented as an array in TypeScript. You add elements 1, 2, 3, then remove two elements. What will be the state of the queue after these operations?

const queue: number[] = [];
queue.push(1);
queue.push(2);
queue.push(3);
queue.shift();
queue.shift();
console.log(queue);

hard

A. [2, 3]

B. [1, 2, 3]

C. [3]

D. []

Solution

1. Step 1: Add elements to queue

   Elements 1, 2, 3 are added in order: queue = [1, 2, 3]

2. Step 2: Remove two elements using shift()

   First shift() removes 1, second shift() removes 2, leaving [3]

3. Final Answer:

   [3] -> Option C

4. Quick Check:

   After two shifts, queue = [3] [OK]

Hint: Each shift() removes one from front [OK]

Common Mistakes:

• Removing elements with pop() instead of shift()
• Expecting queue to be empty after two removals
• Confusing order of elements after removals