Queue vs Stack When to Use Which in DSA Typescript - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add an item to the end of a queue.

DSA Typescript

queue.[1](item);

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

Apop

Bpush

Cenqueue

Dshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'push' which is for stacks or arrays.

Using 'pop' which removes items.

In a queue, adding an item is called enqueue.

2fill in blank

medium

Complete the code to remove the last item from a stack.

DSA Typescript

stack.[1]();

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

Apop

Benqueue

Cdequeue

Dshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'dequeue' which is for queues.

Using 'shift' which removes from the front.

In a stack, removing the last added item is done with pop.

3fill in blank

hard

Fix the error in the code to remove the first item from a queue.

DSA Typescript

queue.[1]();

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

Apush

Bdequeue

Cpop

Dappend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'pop' which removes from the end.

Using 'push' which adds items.

To remove the first item from a queue, use dequeue.

4fill in blank

hard

Fill both blanks to create a stack and add an item.

DSA Typescript

const stack = new [1]();
stack.[2](item);

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

AStack

BQueue

Cpush

Denqueue

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Queue' instead of 'Stack'.

Using 'enqueue' to add to a stack.

We create a Stack and add items using push.

5fill in blank

hard

Fill all three blanks to create a queue, add an item, and remove an item.

DSA Typescript

const queue = new [1]();
queue.[2](item);
const removed = queue.[3]();

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

AQueue

Benqueue

Cdequeue

DStack

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'Stack' instead of 'Queue'.

Using 'push' or 'pop' with queues.

Create a Queue, add with enqueue, and remove with dequeue.

Practice

1. Which data structure should you use when you need to process tasks in the exact order they arrive, like customers waiting in line at a store?

easy

A. Stack

B. Queue

C. Array

D. Tree

Solution

1. Step 1: Understand the order requirement

   Tasks must be processed in the order they arrive, which means first-in, first-out (FIFO).

2. Step 2: Match the data structure to FIFO

   A queue follows FIFO, so it fits the requirement perfectly.

3. Final Answer:

   Queue -> Option B

4. Quick Check:

   FIFO = Queue [OK]

Hint: Use queue for first-in, first-out order [OK]

Common Mistakes:

• Confusing stack (LIFO) with queue (FIFO)
• Choosing array without order guarantees
• Thinking tree fits linear order

2. Which of the following is the correct TypeScript syntax to add an element to the top of a stack implemented as an array named stack?

easy

A. stack.unshift(element);

B. stack.pop(element);

C. stack.shift(element);

D. stack.push(element);

Solution

1. Step 1: Identify stack operation to add element

   Adding to the top of a stack means pushing an element onto it.

2. Step 2: Match with correct array method

   In TypeScript, push() adds an element to the end (top) of the array acting as a stack.

3. Final Answer:

   stack.push(element); -> Option D

4. Quick Check:

   Push adds to stack top [OK]

Hint: Use push() to add on stack top [OK]

Common Mistakes:

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

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

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

medium

A. [3, 2]

B. [1, 2, 3]

C. [2, 3]

D. []

Solution

1. Step 1: Trace queue operations

   Elements 1, 2, 3 are added to the queue using push(). Then shift() removes the first element (1).

2. Step 2: Determine queue state after removal

   After removing 1, the queue contains [2, 3].

3. Final Answer:

   [2, 3] -> Option C

4. Quick Check:

   shift() removes first, queue left with [2, 3] [OK]

Hint: shift() removes front in queue [OK]

Common Mistakes:

• Thinking push adds to front instead of back
• Confusing shift() with pop()
• Expecting stack order instead of queue order

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

const stack: number[] = [];
stack.push(10);
stack.push(20);
const top = stack.shift();
console.log(top);

medium

A. Using shift() instead of pop() to remove top element

B. Using push() instead of unshift() to add element

C. Not initializing the stack array

D. Using console.log incorrectly

Solution

1. Step 1: Identify stack removal method

   Stack removes the top element using pop(), not shift().

2. Step 2: Analyze code's removal method

   The code uses shift(), which removes the first element, breaking stack behavior.

3. Final Answer:

   Using shift() instead of pop() to remove top element -> Option A

4. Quick Check:

   Stack removal = pop(), not shift() [OK]

Hint: Stack removes top with pop(), not shift() [OK]

Common Mistakes:

• Confusing shift() with pop()
• Thinking push() adds to front
• Ignoring array initialization

5. You are designing a system to undo and redo user actions. Which data structure combination is best suited for this, and why?

hard

A. Two stacks: one for undo, one for redo, because stacks allow reversing actions easily

B. Two queues: one for undo, one for redo, because queues maintain order of actions

C. One stack only, because redo is not needed

D. One queue only, because undo and redo are processed in order

Solution

1. Step 1: Understand undo/redo requirements

   Undo and redo require reversing and reapplying actions in last-in, first-out order.

2. Step 2: Match data structures to behavior

   Stacks naturally support LIFO, so using two stacks (undo and redo) allows easy push/pop for these operations.

3. Final Answer:

   Two stacks: one for undo, one for redo, because stacks allow reversing actions easily -> Option A

4. Quick Check:

   Undo/Redo = Two stacks (LIFO) [OK]

Hint: Undo/Redo needs two stacks for LIFO action reversal [OK]

Common Mistakes:

• Using queues which do not reverse order easily
• Ignoring redo functionality
• Using only one data structure