Topic
Queue interview questions
All 4 Queue problems from the curated set, easiest first — a core topic for 9 of the 29 engineering roles.
- Easy
- 2
- Medium
- 1
- Hard
- 1
- Sheets
- 3
What Queue is
Updated 2026-09-09A queue is an orderly checkout line at a grocery store counter where patrons enter at the back and leave from the front. The person who arrives first gets served first, while newcomers wait patiently behind whoever came before them. Unlike a stack which turns back on its latest arrival, a queue preserves fair chronological arrival order, processing tasks strictly from oldest to newest.
When to reach for it
Reach for a queue when exploring states level by level, such as finding the shortest path across an unweighted graph or traversing a tree horizontally. It fits rate-limiting buffers, print spools, asynchronous task schedulers, and sliding cache windows where oldest items expire first. Any problem stating that processing must honor strict time-of-arrival order is an immediate candidate.
How to think about it
Track two distinct ends: an enqueue boundary at the tail and a dequeue boundary at the head. In breadth traversals, snapshot the queue size before starting an inner loop to process an entire depth tier in one grouped wave. Items currently enqueued represent the frontier of known but unresolved states. Ensure newly generated states are marked visited upon insertion rather than upon extraction to prevent duplicated queue entries.
What each operation costs
| Operation | Time |
|---|---|
| enqueue item at the back | O(1) |
| dequeue item from the front | O(1) |
| inspect the front item | O(1) |
What usually goes wrong
- Using a standard dynamic array as a queue and removing from index zero, creating hidden linear shifts on every pop operation.
- Marking tree or graph nodes as visited during dequeue instead of enqueue, causing identical nodes to be repeatedly enqueued and blowing up memory consumption.
- Omitting the snapshot of queue size when running level-order sweeps, resulting in parent nodes and newly added child nodes blending into the same loop round.
Every Queue problem, easiest first
Roles that need Queue
If you are targeting one of these, Queue sits early in your path rather than being optional.
Track Queue in your role's order
Pick your target role and all 370 problems resequence to what that interview actually asks. Free.
Start freeQueue interview questions, answered
How many Queue problems should I solve for interviews?
4 curated Queue problems cover the patterns interviews repeat: 2 easy, 1 medium and 1 hard. They are drawn from 3 widely used sheets, deduplicated, and ordered easiest first.
Is Queue actually asked in coding interviews?
Yes, though how much depends on the role. Queue is a core topic for 9 of the 29 engineering roles tracked here, including SDE / Backend Engineer, Full-Stack Developer, Android Developer. For other roles it is lower frequency and belongs later in a study plan.
Which Queue problem should I start with?
Start with Implement Queue using Stacks (Easy). The list on this page is ordered easiest first for that reason, so working top to bottom builds the pattern before the harder variations arrive.
Other topics
Problem set and role mapping as of .