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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All levels Beginner Intermediate Hard

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1,575 challenges matching your filters

Code AnalysisIntermediate
Orchestration single point
architecturesagaresilience
Code AnalysisBeginner
Shared module creates cycle at package level
architecturemodularitydependencies
Code AnalysisIntermediate
Abstractness/instability zone check
architecturemetricscoupling
Code AnalysisBeginner
Bulkhead absence cascades
architectureresiliencebulkhead
Code AnalysisHard
Idempotency: naive dedupe key
architectureidempotencyconcurrency
Code AnalysisBeginner
Test double misuse
architecturetestingtest-doubles
Code AnalysisIntermediate
Test seam for legacy code
architecturetestingseams
Code AnalysisBeginner
Branch by abstraction setup
architecturerefactoringbranch-by-abstraction
Code AnalysisHard
Aggregate invariants vs eventual consistency
architecturedddconsistency
Code AnalysisBeginner
Value object mutability bug
architecturedddvalue-object
Code AnalysisHard
Anti-corruption layer absence
architecturedddacl
Code AnalysisBeginner
Modular monolith boundary enforcement
architecturemodularitymonolith
Code AnalysisHard
Feature flag interaction bug
architecturefeature-flagstesting
Code AnalysisBeginner
Query side should not be reused for writes
architecturecqrsseparation
Code AnalysisHard
Gateway timeout as circuit breaker signal
architectureresiliencecircuit-breaker
Code AnalysisBeginner
Anemic DTO vs domain object
architecturedddanemic-model
Code AnalysisHard
Repository per aggregate only
architecturedddrepository
Code AnalysisBeginner
Strangler deletion debt
architecturemigrationstrangler-fig
Code AnalysisHard
Event schema evolution break
architectureedaversioning
Code AnalysisBeginner
Dependency injection container misuse
architecturedicoupling
Code AnalysisHard
Saga pivot vs compensation ordering
architecturesagadistributed
Code AnalysisBeginner
Cyclic dependency via event handler
architecturemodularityeda
Code AnalysisBeginner
Analyze: feature envy smell
feature-envytell-dont-askrefactoring
Code AnalysisIntermediate
Analyze: LSP behavioral subtyping break
lspsolidsubtyping
Code AnalysisHard
Analyze: aggregate invariant leak
aggregateinvariantsddd
Code AnalysisIntermediate
Analyze: DIP ownership direction
diprepositoryhexagonal
Code AnalysisIntermediate
Analyze: SRP multiple reasons to change
srpsolidcohesion
Code AnalysisHard
Violated Principle: Layering Leak
layeringdipboundaries
Code AnalysisHard
Projection Rebuild Requirement
event-sourcingprojection-rebuildupcasting
Code AnalysisHard
Saga vs Process Manager
sagaprocess-managerorchestration
Code AnalysisIntermediate
Transactional Boundary Violation
transactionsconsistencyaggregates
Code AnalysisHard
Aggregate Design for Concurrency
aggregatesconcurrencyddd
Code AnalysisHard
Outbox vs CDC
outboxcdcdual-write
Code AnalysisHard
ACL Translation Layer
acldddintegration
Code AnalysisHard
Functional Core, Imperative Shell
functional-coreimperative-shelltestability
Code AnalysisIntermediate
Ports and Adapters Testing
hexagonalports-adapterstestability
Code AnalysisIntermediate
Enforcing Boundaries with ArchUnit
archunitboundariesfitness-functions
Code AnalysisBeginner
Coupling Metrics: Instability
coupling-metricsmartin-metricsdependency-graph
Code AnalysisHard
Conway's Law Implication
conways-laworg-designteam-topologies
Code AnalysisIntermediate
Event Versioning / Upcasting
event-sourcingupcastingversioning
Code AnalysisHard
Multi-Tenancy Isolation Choice
multi-tenancyisolationsilopoolbridge
Code AnalysisIntermediate
Authorization Model Fit
authorizationrebacabac
Code AnalysisBeginner
Policy as Code
policy-as-codeopaauthorization
Code AnalysisHard
Violated principle in subclass override
lspsolidcode-analysis
Code AnalysisHard
Wrong abstraction refactor
wrong-abstractionrefactoringcode-analysis
Code AnalysisBeginner
Abstraction leakage in repository
abstraction-leakagerepositorycode-analysis
Code AnalysisIntermediate
Missing transactional outbox
outboxreliabilitycode-analysis
Code AnalysisIntermediate
Sync engine conflict handling
sync-engineconflict-resolutioncode-analysis
Code AnalysisHard
CRDT operation design
crdtcollaborative-editingcode-analysis
Code AnalysisBeginner
Module boundary violation
module-boundariesbuild-enforcementcode-analysis
Code AnalysisIntermediate
DIP violation via direct SDK import
dipports-and-adapterscode-analysis
Code AnalysisIntermediate
Fat interface / ISP violation
ispsolidcode-analysis
Code AnalysisIntermediate
Composition over inheritance refactor
compositioninheritancecode-analysis
Code AnalysisIntermediate
Template method wrong fit
template-methodstrategycode-analysis
Code AnalysisIntermediate
Strategy vs state selection
statestrategycode-analysis
Code AnalysisIntermediate
Visitor for business rules
visitorpatternscode-analysis
Code AnalysisHard
Rules engine vs hard-coded conditions
rules-enginedecision-tablescode-analysis
Code AnalysisIntermediate
Durable execution vs retries
durable-executionworkflow-enginecode-analysis
Code AnalysisIntermediate
Data contract for analytics eventing
data-contractseventingcode-analysis
Code AnalysisBeginner
What Debt Quadrant Is This
debt-quadranttechnical-debtcode-analysis

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.

Coding Challenges

Orchestration single point

Shared module creates cycle at package level

Abstractness/instability zone check

Bulkhead absence cascades

Idempotency: naive dedupe key

Test double misuse

Test seam for legacy code

Branch by abstraction setup

Aggregate invariants vs eventual consistency

Value object mutability bug

Anti-corruption layer absence

Modular monolith boundary enforcement

Feature flag interaction bug

Query side should not be reused for writes

Gateway timeout as circuit breaker signal

Anemic DTO vs domain object

Repository per aggregate only

Strangler deletion debt

Event schema evolution break

Dependency injection container misuse

Saga pivot vs compensation ordering

Cyclic dependency via event handler

Analyze: feature envy smell

Analyze: LSP behavioral subtyping break

Analyze: aggregate invariant leak

Analyze: DIP ownership direction

Analyze: SRP multiple reasons to change

Violated Principle: Layering Leak

Projection Rebuild Requirement

Saga vs Process Manager

Transactional Boundary Violation

Aggregate Design for Concurrency

Outbox vs CDC

ACL Translation Layer

Functional Core, Imperative Shell

Ports and Adapters Testing

Enforcing Boundaries with ArchUnit

Coupling Metrics: Instability

Conway's Law Implication

Event Versioning / Upcasting

Multi-Tenancy Isolation Choice

Authorization Model Fit

Policy as Code

Violated principle in subclass override

Wrong abstraction refactor

Abstraction leakage in repository

Missing transactional outbox

Sync engine conflict handling

CRDT operation design

Module boundary violation

DIP violation via direct SDK import

Fat interface / ISP violation

Composition over inheritance refactor

Template method wrong fit

Strategy vs state selection

Visitor for business rules

Rules engine vs hard-coded conditions

Durable execution vs retries

Data contract for analytics eventing

What Debt Quadrant Is This

Practice now, dominate the arena