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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1,344 challenges matching your filters
- Code AnalysisHard
Sync replication availability trap
system-designreplicationcap-theorem - Code AnalysisHard
Fan-out-on-write celebrity
system-designnews-feedfan-out - Code AnalysisHard
Split-brain from naive failover
system-designconsensusavailability - Code AnalysisHard
Outbox without proper relay
system-designoutboxdistributed-transactions - Code AnalysisHard
Thundering herd with negative result
system-designcachingcache-penetration - Code AnalysisHard
Unbounded cardinality metric
system-designobservabilitymetrics - Code AnalysisHard
CAS retry livelock
system-designconcurrencydistributed-counter - Code AnalysisHard
Retry without idempotency on a non-idempotent path
system-designidempotencyretry - Code AnalysisHard
At-least-once with side effect before ack
system-designmessagingidempotency - Code AnalysisHard
Fencing missing on lease-based lock
system-designconsensusleader-election - Code AnalysisHard
Backpressure via unbounded broker retention
system-designmessagingbackpressure - Code AnalysisHard
Quorum read after failed write
system-designquorumconsistency - Code AnalysisHard
Idempotency key stored after the effect
system-designidempotencyconcurrency - Code AnalysisHard
Fan-out read amplification
system-designnews-feedfan-out - Code AnalysisHard
Offset commit before processing
system-designmessagingkafka - Code AnalysisHard
Unbounded retry on non-transient error
system-designresilienceretry - Code AnalysisHard
CAS without version on concurrent edit
system-designconcurrencydatabases - Code AnalysisHard
Bloom filter with no eviction
system-designcachingbloom-filter - Code AnalysisHard
Commit before process loses messages
kafkaoffset-commitmessage-loss - Code AnalysisHard
Lost update from read-modify-write
transactionslost-updateconcurrency - Code AnalysisHard
Phantom read with range predicate
phantom-readisolation-levelsmvcc - Code AnalysisHard
LSM write amplification analyzer
lsmcompactionrocksdb - Code AnalysisHard
Two-phase commit blocking analysis
2pcdistributed-transactionsblocking - Code AnalysisHard
Time-Series Cardinality Explosion
metricscardinalitytime-series - Code AnalysisHard
Mutable Balance Ledger Correction
ledgerimmutabilitydouble-entry - Code AnalysisHard
Reconciliation Missing Rows Bug
reconciliationsqlouter-join - Code AnalysisHard
Quiet Hours Suppression Logic Bug
notificationsquiet-hourstimezone - Code AnalysisHard
Chat Ordering by Client Clock
chatorderingclocks - Code AnalysisHard
Edge buffer overflow dropping IoT data
iotedge-bufferingmqtt - Code AnalysisHard
Log query scanning cold tier
log-aggregationquery-at-scaleindexing - Code AnalysisHard
Feature leakage across train/serve
recommendationfeature-storetrain-serve-skew - Code AnalysisHard
Sequential testing without peeking control
experimentationsequential-testingstatistics - Code AnalysisHard
Backfill double-counting aggregates
data-pipelinebackfillidempotency - Code AnalysisHard
Trace assembly with clock skew
tracingtrace-assemblyclock-skew - Code AnalysisHard
KMS secret rotation leaving stale ciphertext
secretsrotationkms - Code AnalysisHard
Hot leaderboard partition on one key
leaderboardhot-partitionredis - Code AnalysisHard
Webhook deliveries without ordering guard
webhooksorderingdlqbackpressure - Multiple ChoiceHard
Compensating transaction design
architecturedistributedsagaidempotency - Multiple ChoiceHard
Outbox pattern
architectureedaoutbox - Multiple ChoiceHard
Technical debt: deliberate vs accidental
architecturetechnical-debtrefactoring - Multiple ChoiceHard
Feature flag debt
architecturefeature-flagstechnical-debt - Multiple ChoiceHard
Boundary leak via shared database
architecturemicroservicescoupling - Multiple ChoiceHard
Thundering herd on cache expiry
architectureresiliencecaching - Multiple ChoiceHard
Backpressure vs dropping
architectureresiliencebackpressure - Multiple ChoiceHard
Consistency boundary choice
architecturedddconsistency - Multiple ChoiceHard
Correlation ids in distributed tracing
architectureobservabilitytracing - Multiple ChoiceHard
Fragile base class problem
architectureoopinheritance - Multiple ChoiceHard
Aggregate size trade-off
architecturedddaggregate - Multiple ChoiceHard
Modularity enforcement
architecturemodularityfitness-functions - Multiple ChoiceHard
Domain service vs application service
architecturedddlayering - Multiple ChoiceHard
Rich model invariant
architecturedddinvariants - Multiple ChoiceHard
Strangler routing: shadow traffic
architecturemigrationstrangler-fig - Multiple ChoiceHard
Service granularity trap
architecturemicroservicesgranularity - Code AnalysisHard
Saga: non-idempotent compensation
architecturedistributedsagaidempotency - Code AnalysisHard
Dual-write inconsistency
architectureedaoutbox - Code AnalysisHard
Facade hides subsystem steps
architecturedesign-patternsfacade - Code AnalysisHard
Thundering herd on expiry
architectureresiliencecaching - Code AnalysisHard
Idempotency: naive dedupe key
architectureidempotencyconcurrency - Code AnalysisHard
Aggregate invariants vs eventual consistency
architecturedddconsistency - Code AnalysisHard
Anti-corruption layer absence
architecturedddacl
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