Questions
10 of 18
What are the basic operations of a Queue? (Enqueue, Dequeue)
Difficulty: 2/10
enqueue, dequeue, queue implementation
Queue Operations
The core Queue operations are Enqueue and Dequeue. Enqueue inserts an element at the rear, while Dequeue removes the element at the front. A production-quality queue should also define operations for inspecting the front and checking whether the queue is empty.
javascript
- 1
Enqueue adds an element to the rear.
- 2
Dequeue removes the oldest element from the front.
- 3
With head and tail pointers, both can be O(1).
- 4
Using an array with repeated removal from index 0 can cause O(n) shifts and should generally be avoided.
- 5
A circular buffer or linked queue provides efficient queue operations.
Scenario Questions
0-2 years experience
- 1Imagine you need to implement a print‑job scheduler that processes jobs in the order they arrive. How would you use enqueue and dequeue to manage the job queue?
- 2If you call dequeue on an empty queue, what should happen and how would you code that case?
- 3Given a circular array implementation, how do you add an element when the tail index reaches the end of the array?
2-5 years experience
- 1Our web server buffers incoming requests in a queue before workers pick them up. One day workers are idle because the queue stops delivering requests. Walk me through how you would debug the enqueue/dequeue logic.
- 2We need to add priority handling while keeping the existing enqueue/dequeue API. What trade‑offs would you consider?
- 3If the queue can grow without bound, what strategies would you use to prevent memory exhaustion while still using basic enqueue and dequeue?
5-8 years experience
- 1Design a high‑throughput messaging system that decouples producers and consumers. How would you make enqueue and dequeue lock‑free and scale to millions of messages per second?
- 2When persisting a queue to disk for crash recovery, what edge cases around enqueue/dequeue ordering must you handle to avoid lost or duplicated messages?
- 3Explain how you would implement back‑pressure when the consumer is slower than the producer, using only enqueue and dequeue primitives.
8+ years experience
- 1Our organization is migrating from an in‑process queue to a distributed message broker. What architectural considerations around the semantics of enqueue and dequeue must be addressed to keep existing services functional?
- 2Multiple teams have different queue implementations (linked list, ring buffer, lock‑free). How would you define a common contract for enqueue/dequeue that supports future extensions like batch operations and observability?
- 3If we need exactly‑once processing across microservices, how does that affect the design of enqueue and dequeue mechanisms at the system level?
Follow-up Questions
- How would you handle concurrent producers and consumers?
- What tests would you write for dequeuing from an empty queue?
- What are the trade‑offs between a linked‑list and an array backing store?