Question Bank

Every question, one list

Sandboxed coding rounds that run against a hidden test suite, and written questions graded against a rubric — side by side, because when you are drilling a topic you want both.

25 questions · browse by bank instead

Design a chat serviceConnection state is the real problem, and ordering is per-conversation, never global.hardWrittenExplain to unlock#consistency#distributed-systems#hld45 min
Design a collaborative document editorThe hardest consistency question on the list. OT versus CRDT, honestly.hardWrittenExplain to unlock#consistency#distributed-systems#hld45 min
Design a distributed job schedulerLeader election and at-least-once done properly, with dependencies.hardWrittenExplain to unlock#distributed-systems#hld#reliability45 min
Design a distributed key-value storeThe question that tests whether you know CAP for real rather than as a slogan.hardWrittenExplain to unlock#consistency#distributed-systems#hld45 min
Design a distributed rate limiterChoosing the algorithm is half of it. The other half is what happens when the limiter itself fails.hardWritten#distributed-systems#rate-limiting#system-design45 min
Design a file sync serviceBandwidth is the constraint, and two offline devices editing the same file is the hard case.hardWrittenExplain to unlock#consistency#hld#storage45 min
Design a limit order bookThe canonical quant LLD question. Choosing the data structure is where it is won or lost.hardWrittenExplain to unlock#data-structures#lld#low-latency45 min
Design a market data distribution systemWhere the usual system-design answers stop working: microseconds matter, and dropping data can be correct.hardWritten#lock-free#low-latency#market-data50 min
Design a metrics and monitoring systemWrite-heavy, and cardinality is what actually kills these systems.hardWrittenExplain to unlock#hld#reliability#storage45 min
Design a news feedThe fanout question, and the most-asked design round in the industry.hardWrittenExplain to unlock#caching#distributed-systems#hld45 min
Design a payment system and ledgerCorrectness over throughput. Money makes every shortcut visible.hardWrittenExplain to unlock#consistency#hld#reliability45 min
Design a post and follow-graph serviceFeed seen from the write path: id generation, the follow graph, and hot keys.hardWrittenExplain to unlock#consistency#distributed-systems#hld45 min
Design a ride-matching serviceGeospatial search plus a very high write rate of location updates.hardWrittenExplain to unlock#distributed-systems#hld#storage45 min
Design a ticket booking systemInventory correctness under a thundering herd. Overselling is the failure to design against.hardWrittenExplain to unlock#concurrency#consistency#hld45 min
Design a video streaming serviceA job pipeline wearing a product costume, plus the economics of delivery.hardWrittenExplain to unlock#caching#hld#queues45 min
Design a web crawlerThe politeness question. Dedup at billions of URLs is where the naive answer breaks.hardWrittenExplain to unlock#distributed-systems#hld#storage45 min
Design an ad click aggregation pipelineThe streaming-correctness question. Late events and duplicates decide the round.hardWrittenExplain to unlock#consistency#hld#queues45 min
Design an object storage serviceDurability arithmetic, and the metadata service that is the real bottleneck.hardWrittenExplain to unlock#hld#reliability#storage45 min
Fewest machines to finish by a deadlineBinary search on the answer. Recognising that the question is monotonic is the whole insight.hardWrittenExplain to unlock#binary-search#greedy#optimisation30 min
Take-home: trade reconciliationTwo files that should agree and do not. A quant-flavoured brief where the edge cases are the whole exercise.hardWritten#correctness#data#take-home300 min
The ABA problemYour compare-and-swap succeeded. That does not mean nothing happened.hardWrittenExplain to unlock#atomics#c++#concurrency25 min
Was double-checked locking ever actually broken?A famous bug, a famous fix, and a much simpler answer almost nobody gives.hardWrittenExplain to unlock#c++#concurrency#memory-model20 min
What does memory_order_relaxed actually guarantee?The question that separates people who have used atomics from people who understand them.hardWrittenExplain to unlock#atomics#c++#concurrency25 min
What is the hardest technical problem you have solved?Half behavioral, half technical depth. The follow-ups go deep, so pick something you genuinely understand.hardWritten#behavioral#star#technical-depth30 min
Why is this query slow?An index exists and is not being used. This question is about whether you read plans or guess.hardWritten#indexing#performance#query-planning30 min