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.
Topicimplementation (105)system-design (24)hld (20)trees (11)distributed-systems (10)arrays-hashing (9)concurrency (9)graphs (9)binary-search (8)consistency (8)dp-1d (8)linked-list (8)reliability (8)storage (8)
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- 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 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 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