Queues (first-in, first-out) in Intro to Computing - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ trace

intermediate

Trace the queue operations

Consider a queue where the following operations happen in order:

1. Enqueue 5
2. Enqueue 10
3. Dequeue
4. Enqueue 15
5. Dequeue

What is the content of the queue after these operations?

A [5, 15]

B [5, 10, 15]

C [15]

D [10, 15]

💡 Hint

Remember, a queue removes items in the order they were added (first-in, first-out).

Initially, the queue is empty. After enqueue 5 and 10, queue is [5, 10]. Dequeue removes 5, queue becomes [10]. Enqueue 15 adds 15 at the end, queue is [10, 15]. Dequeue removes 10, queue becomes [15].

🧠 Conceptual

intermediate

Understanding queue behavior

Which real-life example best represents how a queue works?

A A line of people waiting to buy tickets where the first person in line is served first

B A stack of plates where you take the top plate first

C A bookshelf where you pick any book you want

D A pile of clothes where you pick the last folded item first

💡 Hint

Think about who gets served first in each example.

A queue follows first-in, first-out. The line of people waiting to buy tickets is a perfect example because the first person to get in line is the first to be served.

❓ identification

advanced

Identify the queue operation causing error

Given a queue with elements [1, 2, 3], which operation will cause an error if performed next?

A Dequeue (remove the first element)

B Enqueue 4 (add element 4 at the end)

C Dequeue four times in a row

D Peek (view the first element without removing)

💡 Hint

Think about what happens if you remove more elements than the queue contains.

Options A, B, and C are valid on a queue with elements [1, 2, 3]. Dequeue four times in a row removes 1, 2, 3, then attempts to dequeue from an empty queue, causing an error.

❓ Comparison

advanced

Compare queue and stack behavior

Which statement correctly compares a queue and a stack?

A Both queue and stack remove elements in the order they were added

B Queue removes elements in first-in, first-out order; stack removes elements in last-in, first-out order

C Stack removes elements in first-in, first-out order; queue removes elements in last-in, first-out order

D Queue and stack both remove elements randomly

💡 Hint

Think about which element is removed first in each data structure.

A queue removes the oldest element first (FIFO), while a stack removes the most recently added element first (LIFO).

🚀 Application

expert

Determine the final queue content after mixed operations

A queue starts empty. The following operations happen:

1. Enqueue 'A'
2. Enqueue 'B'
3. Dequeue
4. Enqueue 'C'
5. Enqueue 'D'
6. Dequeue
7. Enqueue 'E'
8. Dequeue

What is the content of the queue after all these operations?

A ['D', 'E']

B ['C', 'D', 'E']

C ['B', 'C', 'D', 'E']

D ['E']

💡 Hint

Track each enqueue and dequeue step carefully, remembering FIFO order.

Step by step:
1. Queue: ['A']
2. Queue: ['A', 'B']
3. Dequeue removes 'A', Queue: ['B']
4. Enqueue 'C', Queue: ['B', 'C']
5. Enqueue 'D', Queue: ['B', 'C', 'D']
6. Dequeue removes 'B', Queue: ['C', 'D']
7. Enqueue 'E', Queue: ['C', 'D', 'E']
8. Dequeue removes 'C', Queue: ['D', 'E']