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
[React] className JavaScript XML syntax
qareactreactqa - Multiple ChoiceBeginner
[React] Self-closing JavaScript XML syntax
qareactreactqa - Multiple ChoiceBeginner
[React] Declare State hook
qareactreactqa - Multiple ChoiceBeginner
[React] Updater State hook
qareactreactqa - Multiple ChoiceBeginner
[React] Batching State hook
qareactreactqa - Multiple ChoiceBeginner
[React] Lazy init State hook
qareactreactqa - Multiple ChoiceBeginner
[React] TypeScript State hook
qareactreactqa - Multiple ChoiceBeginner
[SQL] INNER Combine rows from multiple tables
qasqlsqlqa - Multiple ChoiceBeginner
[SQL] LEFT Combine rows from multiple tables
qasqlsqlqa - Multiple ChoiceBeginner
[SQL] CROSS Combine rows from multiple tables
qasqlsqlqa - Multiple ChoiceBeginner
[SQL] SELF Combine rows from multiple tables
qasqlsqlqa - Multiple ChoiceBeginner
[SQL] LATERAL Combine rows from multiple tables
qasqlsqlqa - Multiple ChoiceBeginner
SRP: finding the second reason to change
architecturesolidsrp - Multiple ChoiceBeginner
LSP and equals/hashCode contract
architecturesolidlsp - Multiple ChoiceBeginner
Strategy vs if/else
architecturedesign-patternsstrategy - Multiple ChoiceBeginner
Factory Method vs Abstract Factory
architecturedesign-patternsfactory - Multiple ChoiceBeginner
Adapter vs Facade
architecturedesign-patternsadapterfacade - Multiple ChoiceBeginner
Command pattern: undo
architecturedesign-patternscommand - Multiple ChoiceBeginner
Strangler Fig core idea
architecturemigrationstrangler-fig - Multiple ChoiceBeginner
Sidecar vs Ambassador
architecturedesign-patternssidecarambassador - Multiple ChoiceBeginner
Bounded context definition
architecturedddbounded-context - Multiple ChoiceBeginner
Entity vs Value Object
architecturedddvalue-object - Multiple ChoiceBeginner
Ports and adapters essence
architecturehexagonalports-adapters - Multiple ChoiceBeginner
Anemic vs rich domain model
architecturedddanemic-model - Multiple ChoiceBeginner
Layered architecture direction
architecturelayering - Multiple ChoiceBeginner
Modular monolith benefit
architecturemonolithmodularity - Multiple ChoiceBeginner
When microservices hurt
architecturemicroservicestrade-offs - Multiple ChoiceBeginner
Hexagonal architecture: the driving side
hexagonalports-adapters - Multiple ChoiceBeginner
Onion architecture: innermost layer
onionclean - Multiple ChoiceBeginner
Pipe-and-filter: filter contract
pipe-and-filtercoupling - Multiple ChoiceBeginner
Microkernel: plugin isolation
microkernelocp - Multiple ChoiceBeginner
Context mapping: shared kernel risk
dddcontext-mappingshared-kernel - Multiple ChoiceBeginner
Aggregate root: external access rule
dddaggregateinvariants - Multiple ChoiceBeginner
Value object: equality semantics
dddvalue-objectentity - Multiple ChoiceBeginner
Domain event vs integration event
ddddomain-eventsintegration-events - Multiple ChoiceBeginner
Anemic domain model symptom
anemic-modelrich-modelanti-pattern - Multiple ChoiceBeginner
Big Ball of Mud root cause
big-ball-of-mudanti-pattern - Multiple ChoiceBeginner
ADR: documenting a decision
adrdocumentation - Multiple ChoiceBeginner
Null Object vs Optional
null-objectpatterns - Multiple ChoiceBeginner
Architectural Fitness Functions
fitness-functionsevolutionary-architectureci - Multiple ChoiceBeginner
Detecting a Distributed Monolith
distributed-monolithdeploymentcoupling - Multiple ChoiceBeginner
Stable Dependencies Principle
coupling-metricsdependency-graphsolid - Multiple ChoiceBeginner
Walking Skeleton Purpose
walking-skeletonincrementaldelivery - Multiple ChoiceBeginner
API Versioning: URI Path
api-versioningrestcompatibility - Multiple ChoiceBeginner
Consumer-Driven Contracts
contract-testingpactcdc - Multiple ChoiceBeginner
Feature Flag Debt
feature-flagstechnical-debtcleanup - Multiple ChoiceBeginner
Trunk-Based Development
trunk-basedgitflowci - Multiple ChoiceBeginner
ATAM Quality Attribute Scenario
atamquality-attributesscenarios - Multiple ChoiceBeginner
Vertical Slice Architecture
vertical-slicemodularitystructure - Multiple ChoiceBeginner
Published Language
published-languagedddintegration - Multiple ChoiceBeginner
Backend for Frontend (BFF)
bffapi-gatewayfrontend - Multiple ChoiceBeginner
Golden Paths
platform-engineeringgolden-pathdx - Multiple ChoiceBeginner
Optimistic UI
optimistic-uieventual-consistencyux - Multiple ChoiceBeginner
Offline-first sync: conflict-free field types
offline-firstcrdtconflict-resolution - Multiple ChoiceBeginner
Conflict resolution UX for field edits
conflict-resolutionuxoffline-first - Multiple ChoiceBeginner
Transaction outbox in modular monolith
outboxmodular-monolithreliability - Multiple ChoiceBeginner
Module boundary enforcement via build
module-boundariesbuild-enforcementci - Multiple ChoiceBeginner
Dependency inversion at package level
dipports-and-adapterspackages - Multiple ChoiceBeginner
Abstraction leakage
abstraction-leakagerepositoryorm - Multiple ChoiceBeginner
Premature abstraction cost
premature-abstractionyagnicomplexity
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.