Challenge Library
Coding Challenges
5,893 curated questions across every arena — browse by topic, then jump into a live 2-minute battle to put them to the test.
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2,721 challenges matching your filters
- Code AnalysisIntermediate
Load shedding priority drop
load-sheddingadmission-controlpriority - Code AnalysisIntermediate
Cache key cardinality explosion
cachingcache-keyscardinality - Code AnalysisIntermediate
WebSocket reconnect storm
websocketreconnectthundering-herd - Code AnalysisIntermediate
Cursor pagination stability bug
paginationcursorfeed - Code AnalysisIntermediate
Non-Idempotent Payment Retry Handler
idempotencypaymentsretries - Code AnalysisIntermediate
Non-Atomic Balance Check SQL
sqlconcurrencytoctou - Code AnalysisIntermediate
At-Least-Once Consumer Duplicate Side Effect
exactly-onceconsumeridempotency - Code AnalysisIntermediate
Notification Dedup Missing TTL
notificationsdeduprace - 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 AnalysisIntermediate
Log dedup dropping distinct events
log-aggregationdedupidempotency - Code AnalysisIntermediate
A/B exposure logged after variant call
experimentationexposure-loggingbias - Code AnalysisIntermediate
Exactly-once violated by non-idempotent sink
data-pipelineexactly-onceidempotency - Code AnalysisIntermediate
JWT introspection missing signature check
identityjwtoidcsecurity - Code AnalysisIntermediate
List-objects ACL check per request
file-storageaclmetadata-db - Multiple ChoiceIntermediate
Eventual consistency read path
architectureedaeventual-consistency - Multiple ChoiceIntermediate
Message ordering and idempotency
architectureedaidempotency - Multiple ChoiceIntermediate
Contract testing goal
architecturetestingcontract-testing - Multiple ChoiceIntermediate
Seams and testability
architecturetestingseams - Multiple ChoiceIntermediate
Branch by abstraction
architecturerefactoringbranch-by-abstraction - Multiple ChoiceIntermediate
Fitness functions
architectureevolutionary-architecturefitness-functions - Multiple ChoiceIntermediate
Feature flags vs branches
architecturefeature-flagscicd - Multiple ChoiceIntermediate
Stable Dependencies Principle
architecturemetricssdp - Multiple ChoiceIntermediate
Idempotency key design
architectureresilienceidempotency - Multiple ChoiceIntermediate
Decorator ordering matters
architecturedesign-patternsdecorator - Multiple ChoiceIntermediate
Strategy vs State
architecturedesign-patternsstrategystate - Multiple ChoiceIntermediate
Bulkhead pattern
architectureresiliencebulkhead - Multiple ChoiceIntermediate
Event-carried state transfer vs notification
architectureedacoupling - Multiple ChoiceIntermediate
Interface versioning in events
architectureedaversioning - Multiple ChoiceIntermediate
Make illegal states unrepresentable
architecturedddtype-modeling - Multiple ChoiceIntermediate
Architecture vs design decision
architecturedecision-making - 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 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 AnalysisIntermediate
Circuit breaker covers wrong scope
architectureresiliencecircuit-breaker - 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 AnalysisIntermediate
Wrong abstraction via forced hierarchy
architectureover-abstractionlsp - 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 AnalysisIntermediate
Backpressure ignored
architectureresiliencebackpressure - Code AnalysisIntermediate
Event sourcing projection replay bug
architectureevent-sourcingprojections - Code AnalysisIntermediate
LSP: widening (not narrowing) can also break
architecturesolidlsp - Code AnalysisIntermediate
Contract regression: additive vs breaking
architectureapiversioningbackward-compatibility - Code AnalysisIntermediate
Orchestration single point
architecturesagaresilience - Code AnalysisIntermediate
Abstractness/instability zone check
architecturemetricscoupling - Code AnalysisIntermediate
Test seam for legacy code
architecturetestingseams - Code AnalysisIntermediate
Analyze: LSP behavioral subtyping break
lspsolidsubtyping - Code AnalysisIntermediate
Analyze: DIP ownership direction
diprepositoryhexagonal - Code AnalysisIntermediate
Analyze: SRP multiple reasons to change
srpsolidcohesion
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