What is a queue?
Why Interviewers Ask This
Foundational questions like this help interviewers calibrate the rest of the interview. A confident, accurate answer signals that you have solid Data Structures & Algorithms basics — a prerequisite for any developer role.
Answer
A queue is a linear data structure following the FIFO (First In, First Out) principle — the first element inserted is the first one removed, like a line of people at a counter. Operations: enqueue(item) — add to rear: O(1); dequeue() — remove from front: O(1); peek()/front() — view front without removing: O(1); isEmpty(): O(1). Implementation: array with two pointers (front/rear) — circular buffer to avoid shifting; linked list (enqueue at tail, dequeue at head). Variants: Circular queue — wraps around using modulo; Double-ended queue (Deque) — insert/remove from both ends; Priority queue — elements dequeued by priority (not insertion order), implemented with a heap; Blocking queue — used in concurrent programming, blocks when empty or full. Applications: (1) BFS traversal of graphs and trees; (2) Process scheduling in OS (CPU queue); (3) Print spooler; (4) Message queues (RabbitMQ, Kafka); (5) Level-order tree traversal; (6) Cache eviction (FIFO). Use queues when order of processing must match order of arrival.
Pro Tip
If you're unsure about a detail, say so honestly and explain your reasoning. Interviewers respect candidates who can think through uncertainty rather than bluffing.