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.
Filter by type
Filter by difficulty
Popular topics
61 challenges matching your filters
Clear topic filter- Multiple ChoiceIntermediate
OCP with real trade-offs
architecturesolidocp - Multiple ChoiceIntermediate
LSP: the invariant about preconditions
architecturesolidlsp - Multiple ChoiceIntermediate
ISP: fat interface vs client-specific ports
architecturesolidisp - Multiple ChoiceIntermediate
DIP: direction of dependency arrows
architecturesoliddiphexagonal - Multiple ChoiceIntermediate
OCP via data, not classes
architecturesolidocp - Multiple ChoiceIntermediate
DIP and the composition root
architecturesoliddip - Multiple ChoiceIntermediate
Tell, Don't Ask vs getters
architecturesolidencapsulation - Multiple ChoiceIntermediate
Decorator vs inheritance
architecturedesign-patternsdecorator - Multiple ChoiceIntermediate
Repository vs DAO
architecturedesign-patternsrepository - Multiple ChoiceIntermediate
Circuit breaker states
architectureresiliencecircuit-breaker - Multiple ChoiceIntermediate
Choreography vs orchestration
architecturedistributedsagaeda - Multiple ChoiceIntermediate
CQRS read model
architecturecqrseventual-consistency - Multiple ChoiceIntermediate
Afferent vs efferent
architecturemetricscoupling - Multiple ChoiceIntermediate
Cohesion vs coupling goal
architecturecohesioncoupling - Multiple ChoiceIntermediate
Connascence dynamic
architecturecouplingconnascence - Multiple ChoiceIntermediate
Domain events vs integration events
architecturedddevents - Multiple ChoiceIntermediate
Clean architecture dependency rule
architectureclean-architecturelayering - Multiple ChoiceIntermediate
Distributed monolith anti-pattern
architecturemicroservicesanti-pattern - Multiple ChoiceIntermediate
Microservice prerequisites
architecturemicroservices - Multiple ChoiceIntermediate
Conway's Law implication
architectureconwayorganization - 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
Practice now, dominate the arena
Every challenge here is drawn from the live Code Royale pool. Review a question, then head to the arena to answer under pressure against a real opponent — 3-minute matches, Elo ranking, and badge tiers on the line.