Challenge Library
Coding Challenges
5,893 curated questions across every arena — browse by topic, then jump into a live 3-minute battle to put them to the test.
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Clear topic filter- Code AnalysisIntermediate
Hot key in a cache cluster
system-designcachinghot-partition - Code AnalysisIntermediate
Consistent hashing with few vnodes
system-designconsistent-hashingload-balancing - Code AnalysisHard
Retry without idempotency on a non-idempotent path
system-designidempotencyretry - Code AnalysisIntermediate
Deadlock from lock ordering
system-designdatabasesconcurrency - Code AnalysisHard
At-least-once with side effect before ack
system-designmessagingidempotency - Code AnalysisIntermediate
Read-through stampede on cold start
system-designcachingstampede - Code AnalysisHard
Fencing missing on lease-based lock
system-designconsensusleader-election - Code AnalysisIntermediate
Selective column over-fetch
system-designdatabasesperformance - Code AnalysisHard
Backpressure via unbounded broker retention
system-designmessagingbackpressure - Code AnalysisIntermediate
Negative caching with wrong TTL
system-designcachingttl - Code AnalysisBeginner
No timeout on downstream call
system-designavailabilityresilience - Code AnalysisIntermediate
Double-write to cache and DB
system-designcachingcache-invalidation - Code AnalysisHard
Quorum read after failed write
system-designquorumconsistency - Code AnalysisBeginner
Unbounded result set in API
system-designapi-designpagination - Code AnalysisHard
Idempotency key stored after the effect
system-designidempotencyconcurrency - Code AnalysisBeginner
Fixed-window boundary burst
system-designrate-limiting - Code AnalysisHard
Fan-out read amplification
system-designnews-feedfan-out - Code AnalysisIntermediate
Queue with no DLQ and infinite retry
system-designmessagingdlq - Code AnalysisBeginner
Read-modify-write without atomicity
system-designconcurrencydistributed-counter - Code AnalysisIntermediate
Fire-and-forget event loss
system-designmessagingoutbox - Code AnalysisIntermediate
Thundering herd from synchronized cron
system-designcachingstampede - Code AnalysisBeginner
Writing to a replica
system-designdatabasesreplication - Code AnalysisHard
Offset commit before processing
system-designmessagingkafka - Code AnalysisIntermediate
Cache write without invalidation on update
system-designcachingcache-invalidation - Code AnalysisHard
Unbounded retry on non-transient error
system-designresilienceretry - Code AnalysisIntermediate
In-memory session per instance
system-designscalabilitystateless - Code AnalysisHard
CAS without version on concurrent edit
system-designconcurrencydatabases - Code AnalysisIntermediate
Sync call in an async event loop
system-designscalabilityconcurrency - Code AnalysisHard
Bloom filter with no eviction
system-designcachingbloom-filter - Code AnalysisIntermediate
Chatty microservice call
system-designmicroservicesperformance
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