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
1,300 challenges matching your filters
- 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 - Multiple ChoiceBeginner
Rule of three
rule-of-threerefactoringdry - Multiple ChoiceBeginner
Composition over inheritance pitfalls
compositioninheritancecoupling - Multiple ChoiceBeginner
ISP and fat interfaces
ispsolidinterfaces - Multiple ChoiceBeginner
Hexagonal adapters for third-party SDKs
hexagonaladapterthird-party - Multiple ChoiceBeginner
Adapter vs facade
adapterfacadepatterns - Multiple ChoiceBeginner
Strategy vs state vs policy
strategystatepatterns - Multiple ChoiceBeginner
Template method vs strategy
template-methodstrategypatterns - Multiple ChoiceBeginner
What an ADR Records
adrdocumentationdecision-records - Multiple ChoiceBeginner
Cost of Change Meaning
cost-of-changeeconomicsarchitecture - Multiple ChoiceBeginner
Technical Debt Definition
technical-debtarchitecturetradeoffs - Multiple ChoiceBeginner
The Technical Debt Quadrant
debt-quadranttechnical-debtfowler - Multiple ChoiceBeginner
Deliberate vs Accidental Debt
technical-debtdeliberate-debtdebt-quadrant - Multiple ChoiceBeginner
Reversibility of Decisions
reversibilitydecisionstradeoffs - Multiple ChoiceBeginner
Just-In-Time Architecture
just-in-timelean-architecturedecisions - Multiple ChoiceBeginner
YAGNI at Architecture Level
yagnisimplicityarchitecture - Multiple ChoiceBeginner
C4 Model Diagram Levels
c4-modeldiagramsdocumentation - Multiple ChoiceBeginner
Canary vs Blue-Green Deployment
progressive-deliverycanaryblue-green - Multiple ChoiceBeginner
Parallel Change for APIs
parallel-changeexpand-contractapi-evolution - Multiple ChoiceBeginner
Stateless services and sticky sessions
system-designscalability - Multiple ChoiceBeginner
Vertical vs horizontal scaling limit
system-designscalability - Multiple ChoiceBeginner
L4 vs L7 load balancer
system-designload-balancing - Multiple ChoiceBeginner
Consistent hashing vs modulo hashing
system-designload-balancingconsistent-hashing - Multiple ChoiceBeginner
Cache-aside vs write-through
system-designcaching - Multiple ChoiceBeginner
Write-back cache risk
system-designcaching - Multiple ChoiceBeginner
LRU vs LFU eviction
system-designcachingeviction - Multiple ChoiceBeginner
Negative caching
system-designcaching - Multiple ChoiceBeginner
CDN purpose
system-designcachingcdn - Multiple ChoiceBeginner
Cache penetration
system-designcaching - Multiple ChoiceBeginner
Read replica lag
system-designdatabasesreplication - Multiple ChoiceBeginner
SQL vs NoSQL access pattern
system-designdatabasesnosql - Multiple ChoiceBeginner
Index write amplification
system-designdatabasesindexes - Multiple ChoiceBeginner
Leader election with consensus
system-designconsensusleader-election - Multiple ChoiceBeginner
CAP theorem statement
system-designcap-theorem - Multiple ChoiceBeginner
Causal consistency
system-designconsistency - Multiple ChoiceBeginner
Eventual consistency tradeoff
system-designconsistency - Multiple ChoiceBeginner
At-least-once semantics
system-designmessagingidempotency - Multiple ChoiceBeginner
Dead letter queue
system-designmessagingdlq - Multiple ChoiceBeginner
Poison message and head-of-line blocking
system-designmessagingdlq - Multiple ChoiceBeginner
Token bucket burst behavior
system-designrate-limiting - Multiple ChoiceBeginner
Sliding window log memory cost
system-designrate-limiting - Multiple ChoiceBeginner
Cursor vs offset pagination
system-designapi-designpagination - Multiple ChoiceBeginner
API versioning rationale
system-designapi-designversioning - Multiple ChoiceBeginner
SLI vs SLO vs SLA
system-designobservabilityslo - Multiple ChoiceBeginner
p99 vs mean latency
system-designobservabilitylatency - Multiple ChoiceBeginner
Blob vs object storage
system-designstorages3 - Multiple ChoiceBeginner
Inverted index
system-designsearchinverted-index - Multiple ChoiceBeginner
URL shortener key generation
system-designurl-shortenerunique-id
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.