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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1,575 challenges matching your filters
- Code AnalysisIntermediate
At-Least-Once Consumer Duplicate Side Effect
exactly-onceconsumeridempotency - Code AnalysisHard
Reconciliation Missing Rows Bug
reconciliationsqlouter-join - Code AnalysisIntermediate
Notification Dedup Missing TTL
notificationsdeduprace - Code AnalysisHard
Quiet Hours Suppression Logic Bug
notificationsquiet-hourstimezone - Code AnalysisHard
Chat Ordering by Client Clock
chatorderingclocks - Code AnalysisIntermediate
Feature Flag Inconsistent Rollout Seed
feature-flagsrolloutconsistency - Code AnalysisIntermediate
Tenant filter missing in query
multi-tenantisolationsql - Code AnalysisIntermediate
Unbounded tenant metric key cardinality
iotcardinalitymetrics - Code AnalysisHard
Edge buffer overflow dropping IoT data
iotedge-bufferingmqtt - Code AnalysisIntermediate
Log dedup dropping distinct events
log-aggregationdedupidempotency - Code AnalysisHard
Log query scanning cold tier
log-aggregationquery-at-scaleindexing - Code AnalysisHard
Feature leakage across train/serve
recommendationfeature-storetrain-serve-skew - Code AnalysisIntermediate
A/B exposure logged after variant call
experimentationexposure-loggingbias - Code AnalysisHard
Sequential testing without peeking control
experimentationsequential-testingstatistics - Code AnalysisIntermediate
Exactly-once violated by non-idempotent sink
data-pipelineexactly-onceidempotency - Code AnalysisHard
Backfill double-counting aggregates
data-pipelinebackfillidempotency - Code AnalysisHard
Trace assembly with clock skew
tracingtrace-assemblyclock-skew - Code AnalysisIntermediate
JWT introspection missing signature check
identityjwtoidcsecurity - Code AnalysisHard
KMS secret rotation leaving stale ciphertext
secretsrotationkms - Code AnalysisIntermediate
List-objects ACL check per request
file-storageaclmetadata-db - Code AnalysisHard
Hot leaderboard partition on one key
leaderboardhot-partitionredis - Code AnalysisHard
Webhook deliveries without ordering guard
webhooksorderingdlqbackpressure - Code AnalysisBeginner
Anemic model allows invalid state
architecturedddanemic-model - Code AnalysisIntermediate
Violated LSP with strengthened precondition
architecturesolidlsp - Code AnalysisIntermediate
Circular dependency between modules
architecturemodularitydependencies - Code AnalysisIntermediate
Wrong abstraction: premature interface
architectureover-abstractiondi - Code AnalysisIntermediate
Coupling leak: vendor type in domain
architecturesoliddiphexagonal - Code AnalysisIntermediate
Observer memory leak
architecturedesign-patternsobserver - Code AnalysisBeginner
SRP: god class
architecturesolidsrp - Code AnalysisIntermediate
Unit of Work spanning aggregates
architecturedddunit-of-work - Code AnalysisIntermediate
Strategy gone wrong: enum switch
architecturesolidocp - Code AnalysisIntermediate
Eventual consistency bug after write
architecturecqrseventual-consistency - Code AnalysisIntermediate
Decorator vs subclass explosion
architecturedesign-patternsdecorator - Code AnalysisHard
Saga: non-idempotent compensation
architecturedistributedsagaidempotency - Code AnalysisIntermediate
Circuit breaker covers wrong scope
architectureresiliencecircuit-breaker - Code AnalysisHard
Dual-write inconsistency
architectureedaoutbox - Code AnalysisBeginner
LSP: equals/hashCode mismatch
architecturesolidlsp - Code AnalysisBeginner
Coupling metric read
architecturemetricscoupling - Code AnalysisIntermediate
Fitness function for layering
architecturefitness-functionshexagonal - Code AnalysisIntermediate
Repository leaking persistence
architecturedesign-patternsrepository - Code AnalysisIntermediate
Aggregate reference by object
architecturedddaggregate - Code AnalysisIntermediate
Strangler with broken routing
architecturemigrationstrangler-fig - Code AnalysisHard
Facade hides subsystem steps
architecturedesign-patternsfacade - Code AnalysisIntermediate
Wrong abstraction via forced hierarchy
architectureover-abstractionlsp - Code AnalysisBeginner
Command with undo
architecturedesign-patternscommand - Code AnalysisIntermediate
Ambassador vs Sidecar use
architecturedesign-patternssidecarambassador - Code AnalysisIntermediate
Adapter vs Facade distinction by code
architecturedesign-patternsadapter - Code AnalysisIntermediate
Bounded context language clash
architecturedddbounded-context - Code AnalysisBeginner
Feature flag stale branch
architecturefeature-flagstechnical-debt - Code AnalysisIntermediate
Backpressure ignored
architectureresiliencebackpressure - Code AnalysisBeginner
Command/query separation violation
architecturecqrsprinciples - Code AnalysisBeginner
ISP in a module interface
architecturesolidisp - Code AnalysisIntermediate
Event sourcing projection replay bug
architectureevent-sourcingprojections - Code AnalysisBeginner
CQRS lag breaks read-your-writes
architecturecqrseventual-consistency - Code AnalysisHard
Thundering herd on expiry
architectureresiliencecaching - Code AnalysisBeginner
Anemic model with validation elsewhere
architecturedddanemic-model - Code AnalysisIntermediate
LSP: widening (not narrowing) can also break
architecturesolidlsp - Code AnalysisBeginner
Dependency inversion missing in service
architecturesoliddip - Code AnalysisIntermediate
Contract regression: additive vs breaking
architectureapiversioningbackward-compatibility - Code AnalysisBeginner
Choreography observability gap
architectureedasaga
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