The short answer
A DSA mock interview is a timed practice coding round where you solve one or two data structures and algorithms problems out loud while an experienced engineer plays the interviewer. On Revvox it lasts 60 minutes on video with a shared code pad, and you are marked 1 to 5 on problem solving, code quality, testing and edge cases, complexity, and communication. The written report arrives within 24 hours. A single round costs ₹2,499 ($32).
What a DSA and coding round tests
A coding round looks like a test of whether you know the answer. It is really a test of how you get there. The interviewer gives you a problem, usually about arrays, strings, trees, graphs or dynamic programming, and watches how you understand it, pick an approach, write working code and check it, all while explaining your thinking.
Getting to an accepted solution matters, but so does the route. A candidate who starts with a simple correct approach, says why it is slow, and then improves it often scores better than one who jumps straight to a clever answer they cannot explain. At junior levels the focus is clean, correct code. At senior levels interviewers expect you to reach a good complexity quickly, handle edge cases without prompting, and write code that someone else could maintain.
How it is scored
After the 60-minute round, the interviewer marks each line below 1 to 5 in your written report, due within 24 hours, with notes on what you said and wrote behind each mark. The verdict is one of Strong hire, Hire, Lean hire, Lean no hire or No hire.
| Skill (1 to 5) | What the interviewer looks for |
|---|---|
| Problem solving | You clarify the problem, find a working approach, improve it with a reason, and take hints without losing your way. |
| Code quality | Readable code with clear names, small helper functions where they help, and no tangle of special cases. |
| Testing and edge cases | You trace the code on an example and on the awkward inputs: empty, one item, duplicates, very large values. You catch your own bugs. |
| Complexity | You state time and space cost correctly, know which part dominates, and can say what a faster approach would need. |
| Communication | You explain before you type, keep the interviewer with you, and finish within the time. |
DSA practice questions
Problems in the style of real coding rounds, written by us. In a mock, the interviewer picks one at your level and changes it as you go, so use these to warm up, not to memorise.
- Given a list of meeting start and end times, find the smallest number of rooms needed so no two meetings in one room overlap.Sorting plus a heap or two pointers, and handling meetings that end exactly when another starts.
- Given a string, find the length of the longest stretch with no repeated character.A sliding window with a map of last positions, and a clear explanation of when the window moves.
- A warehouse grid has shelves and open cells. Find the shortest walk from the entrance to every open cell.Breadth-first search from one source, marking visited cells, and the cost in terms of grid size.
- Given the prices of a share over several days, find the best profit with at most two buy-and-sell pairs.A dynamic programming state you can explain in one sentence, then reducing memory to a few variables.
- Merge several sorted lists of user events into one sorted stream.A min-heap of the current head of each list, and its cost compared with merging pairs.
- Given a binary tree, return the values you would see looking at it from the right side.Level-order traversal or a depth-first walk that tracks depth, and a clean base case.
- Given an array of positive numbers and a target, count the subarrays whose sum equals the target, then handle negative numbers too.Why the sliding window stops working with negatives, and switching to prefix sums with a hash map.
How a Revvox DSA mock runs
- Five minutes: the problem. The interviewer reads out a problem at your level. You restate it, ask about input sizes and edge cases, and agree an example.
- Ten minutes: the approach. You talk through a first idea and its cost, then a better one. The interviewer may nudge you, as a real one would.
- Twenty-five minutes: the code. You write the solution in a shared code pad in the language you choose, then walk through it on your example and the tricky cases.
- Ten minutes: a follow-up. A twist on the problem or a second, shorter question: a new constraint, a larger input, or a request to save memory.
- Ten minutes: feedback out loud. The interviewer tells you how it went while it is fresh. The written report, with marks and next steps, follows within 24 hours.
How to prepare in two weeks
Solving hundreds of problems silently is not the same as passing a round. Interviews reward patterns you can recognise quickly and explain clearly, so spend your time on both.
- Learn the patterns, not the problems: two pointers, sliding window, hashing, binary search on the answer, BFS and DFS, heaps, intervals, and the common dynamic programming shapes.
- For each pattern, solve three problems and say out loud why the pattern fits. That sentence is what the interviewer wants to hear.
- Practise in a plain editor without autocomplete or a run button, the way many rounds are held.
- Always state the time and space complexity before the interviewer asks.
- Do at least one timed round with another person watching. Nerves change how you code, and only practice under pressure shows you how.
Common mistakes we see
- Coding before agreeing the approach, then rewriting halfway through when it turns out to be wrong.
- Not asking about input sizes, so the solution is too slow for the real constraints.
- Forgetting empty inputs, single elements, duplicates and negative numbers until the interviewer points them out.
- Long silences. The interviewer cannot give credit for thinking they cannot hear.
- Declaring the code done without tracing it through an example.