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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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4,318 challenges matching your filters
- Multiple ChoiceHard
[SQL] Snapshot Multi-Version Concurrency Control
qasqlsqlqa - Multiple ChoiceHard
[SQL] xmin/xmax Multi-Version Concurrency Control
qasqlsqlqa - Multiple ChoiceHard
[SQL] Vacuum Multi-Version Concurrency Control
qasqlsqlqa - Multiple ChoiceHard
[SQL] XID wraparound Multi-Version Concurrency Control
qasqlsqlqa - Multiple ChoiceHard
[SQL] HOT Multi-Version Concurrency Control
qasqlsqlqa - Multiple ChoiceIntermediate
[SQL] 1NF Reduce redundancy
qasqlsqlqa - Multiple ChoiceIntermediate
[SQL] 2NF Reduce redundancy
qasqlsqlqa - Multiple ChoiceIntermediate
[SQL] 3NF Reduce redundancy
qasqlsqlqa - Multiple ChoiceIntermediate
[SQL] BCNF Reduce redundancy
qasqlsqlqa - Multiple ChoiceIntermediate
[SQL] Denormalize Reduce redundancy
qasqlsqlqa - Multiple ChoiceHard
[SQL] ROW_NUMBER OVER() clause
qasqlsqlqa - Multiple ChoiceHard
[SQL] RANK OVER() clause
qasqlsqlqa - Multiple ChoiceHard
[SQL] LAG/LEAD OVER() clause
qasqlsqlqa - Multiple ChoiceHard
[SQL] Running sum OVER() clause
qasqlsqlqa - Multiple ChoiceHard
[SQL] PARTITION BY OVER() clause
qasqlsqlqa - Multiple ChoiceBeginner
SRP: finding the second reason to change
architecturesolidsrp - 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 ChoiceHard
SOLID is not a checklist
architecturesolidover-abstraction - Multiple ChoiceIntermediate
OCP via data, not classes
architecturesolidocp - Multiple ChoiceBeginner
LSP and equals/hashCode contract
architecturesolidlsp - Multiple ChoiceIntermediate
DIP and the composition root
architecturesoliddip - Multiple ChoiceIntermediate
Tell, Don't Ask vs getters
architecturesolidencapsulation - Multiple ChoiceBeginner
Strategy vs if/else
architecturedesign-patternsstrategy - Multiple ChoiceHard
Observer and memory leaks
architecturedesign-patternsobserver - Multiple ChoiceBeginner
Factory Method vs Abstract Factory
architecturedesign-patternsfactory - Multiple ChoiceBeginner
Adapter vs Facade
architecturedesign-patternsadapterfacade - Multiple ChoiceIntermediate
Decorator vs inheritance
architecturedesign-patternsdecorator - Multiple ChoiceBeginner
Command pattern: undo
architecturedesign-patternscommand - Multiple ChoiceIntermediate
Repository vs DAO
architecturedesign-patternsrepository - Multiple ChoiceHard
Unit of Work and aggregate boundaries
architecturedesign-patternsunit-of-workddd - Multiple ChoiceIntermediate
Circuit breaker states
architectureresiliencecircuit-breaker - Multiple ChoiceHard
Saga vs 2PC
architecturedistributedsaga - Multiple ChoiceIntermediate
Choreography vs orchestration
architecturedistributedsagaeda - Multiple ChoiceIntermediate
CQRS read model
architecturecqrseventual-consistency - Multiple ChoiceHard
Event sourcing: projections and replay
architectureevent-sourcing - Multiple ChoiceBeginner
Strangler Fig core idea
architecturemigrationstrangler-fig - Multiple ChoiceBeginner
Sidecar vs Ambassador
architecturedesign-patternssidecarambassador - Multiple ChoiceHard
Instability I = Ce/(Ca+Ce)
architecturemetricscoupling - Multiple ChoiceHard
Abstractness and the main sequence
architecturemetricscoupling - Multiple ChoiceIntermediate
Afferent vs efferent
architecturemetricscoupling - Multiple ChoiceIntermediate
Cohesion vs coupling goal
architecturecohesioncoupling - Multiple ChoiceIntermediate
Connascence dynamic
architecturecouplingconnascence - Multiple ChoiceBeginner
Bounded context definition
architecturedddbounded-context - Multiple ChoiceHard
Aggregate = transaction boundary
architecturedddaggregate - Multiple ChoiceBeginner
Entity vs Value Object
architecturedddvalue-object - Multiple ChoiceHard
Anti-corruption layer purpose
architecturedddacl - Multiple ChoiceIntermediate
Domain events vs integration events
architecturedddevents - Multiple ChoiceHard
Aggregate reference by id
architecturedddaggregate - Multiple ChoiceBeginner
Ports and adapters essence
architecturehexagonalports-adapters - Multiple ChoiceIntermediate
Clean architecture dependency rule
architectureclean-architecturelayering - Multiple ChoiceBeginner
Anemic vs rich domain model
architecturedddanemic-model - Multiple ChoiceBeginner
Layered architecture direction
architecturelayering - Multiple ChoiceBeginner
Modular monolith benefit
architecturemonolithmodularity - Multiple ChoiceIntermediate
Distributed monolith anti-pattern
architecturemicroservicesanti-pattern - Multiple ChoiceIntermediate
Microservice prerequisites
architecturemicroservices - Multiple ChoiceIntermediate
Conway's Law implication
architectureconwayorganization - Multiple ChoiceBeginner
When microservices hurt
architecturemicroservicestrade-offs
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