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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1,828 challenges matching your filters
- Multiple ChoiceBeginner
[TypeScript] String Named constants
qatypescripttypescriptqa - Multiple ChoiceBeginner
[TypeScript] const enum Named constants
qatypescripttypescriptqa - Multiple ChoiceBeginner
[TypeScript] Reverse mapping Named constants
qatypescripttypescriptqa - Multiple ChoiceBeginner
[TypeScript] Ambient Named constants
qatypescripttypescriptqa - Multiple ChoiceBeginner
[Webpack] devServer Development experience
qawebpackwebpackqa - Multiple ChoiceBeginner
[Webpack] Proxy Development experience
qawebpackwebpackqa - Multiple ChoiceBeginner
[Webpack] HMR Development experience
qawebpackwebpackqa - Multiple ChoiceBeginner
[Webpack] Host/port Development experience
qawebpackwebpackqa - Multiple ChoiceBeginner
[Webpack] Watch Development experience
qawebpackwebpackqa - Multiple ChoiceBeginner
[Webpack] Entry Define build start and end
qawebpackwebpackqa - Multiple ChoiceBeginner
[Webpack] Output Define build start and end
qawebpackwebpackqa - Multiple ChoiceBeginner
[Webpack] Multiple entries Define build start and end
qawebpackwebpackqa - Multiple ChoiceBeginner
[Webpack] PublicPath Define build start and end
qawebpackwebpackqa - Multiple ChoiceBeginner
[Webpack] Hash in filename Define build start and end
qawebpackwebpackqa - Code AnalysisBeginner
NULL comparison bug
system-designdatabasessql - Code AnalysisBeginner
Unbounded SELECT without index
system-designdatabasesindexesreplication - Code AnalysisBeginner
Missing index on a foreign-key join
system-designdatabasesindexes - Code AnalysisBeginner
Cache key without entity version
system-designcachingcache-invalidation - Code AnalysisBeginner
Thundering herd on connection pool resize
system-designdatabasesconnection-pool - Code AnalysisBeginner
Read replica lag on user update
system-designreplicationconsistency - Code AnalysisBeginner
Snowflake clock rollback
system-designunique-idsnowflake - Code AnalysisBeginner
No timeout on downstream call
system-designavailabilityresilience - Code AnalysisBeginner
Unbounded result set in API
system-designapi-designpagination - Code AnalysisBeginner
Fixed-window boundary burst
system-designrate-limiting - Code AnalysisBeginner
Read-modify-write without atomicity
system-designconcurrencydistributed-counter - Code AnalysisBeginner
Writing to a replica
system-designdatabasesreplication - Code AnalysisBeginner
Cache aside stampede on hot key expiry
cachingstampedehot-key - Code AnalysisBeginner
Rebalance storm from long processing
kafkarebalanceconsumer-groups - Code AnalysisBeginner
N+1 query in ORM loop
ormn+1query-optimization - Code AnalysisBeginner
Index-killing function on column
indexingsargabilitysql - Code AnalysisBeginner
Window boundary allows double rate
rate-limitingfixed-windowburst - Code AnalysisBeginner
GCRA smoothness tuning
gcrarate-limitingsmoothing - Code AnalysisBeginner
Ledger double-entry balance check
ledgerdouble-entryinvariants - Code AnalysisBeginner
Kafka per-key ordering pitfall
kafkaorderingpartitioning - Code AnalysisBeginner
Stale-while-revalidate cache bug
cachingswrcdn - Code AnalysisBeginner
Count-min heavy hitters shape
count-minheavy-hitterssketch - Code AnalysisBeginner
Transactional Outbox Pattern for Payments
outboxpaymentsevents - Code AnalysisBeginner
Saga Compensation for Money Transfer
sagatransfercompensation - Code AnalysisBeginner
Notification Fan-Out Deduplication
notificationsdedupretries - Code AnalysisBeginner
Geospatial Index for Ride Matching
ride-hailinggeospatialmatching - Code AnalysisBeginner
Trie Top-K for Search Autocomplete
autocompletetrietop-k - Code AnalysisBeginner
Dual Write Ledger and Event Bug
outboxdual-writeevents - Multiple ChoiceBeginner
API versioning: additive change
architectureapiversioningbackward-compatibility - Multiple ChoiceBeginner
Test pyramid rationale
architecturetestingtest-pyramid - Multiple ChoiceBeginner
Stub vs mock vs fake
architecturetestingtest-doubles - Multiple ChoiceBeginner
Dependency injection benefit
architecturetestingdi - Multiple ChoiceBeginner
ADRs purpose
architectureadrdocumentation - Multiple ChoiceBeginner
Cyclic dependencies harm
architecturemodularitydependencies - Multiple ChoiceBeginner
Package cohesion: CCP
architecturemodularitycohesion - Multiple ChoiceBeginner
Facade reduces coupling
architecturedesign-patternsfacade - Multiple ChoiceBeginner
Cross-cutting logging
architecturecross-cuttinglogging - Multiple ChoiceBeginner
Config as external concern
architectureconfigurationtwelve-factor - Multiple ChoiceBeginner
Composition over inheritance
architectureoopcomposition - Multiple ChoiceBeginner
Anti-corruption in practice
architecturedddacl - Multiple ChoiceBeginner
Port naming by role
architecturehexagonalnaming - Code AnalysisBeginner
Anemic model allows invalid state
architecturedddanemic-model - Code AnalysisBeginner
SRP: god class
architecturesolidsrp - Code AnalysisBeginner
LSP: equals/hashCode mismatch
architecturesolidlsp - Code AnalysisBeginner
Coupling metric read
architecturemetricscoupling - Code AnalysisBeginner
Command with undo
architecturedesign-patternscommand
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