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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702 challenges matching your filters
- Code AnalysisIntermediate
Offset pagination instability
system-designapi-designpagination - Code AnalysisIntermediate
Double-charge on retry
system-designidempotencyapi-design - Code AnalysisIntermediate
Consumer without dedup
system-designmessagingidempotency - Code AnalysisIntermediate
Local rate limiter drift
system-designrate-limitingdistributed - Code AnalysisIntermediate
Full table lock from a long transaction
system-designdatabasesconcurrency - Code AnalysisIntermediate
Unbounded in-memory queue
system-designmessagingbackpressure - Code AnalysisIntermediate
Health check that lies
system-designhealth-checks - Code AnalysisIntermediate
2PC coordinator down
system-designdistributed-transactions2pc - Code AnalysisIntermediate
Exactly-once assumption in consumer
system-designmessagingsqsidempotency - Code AnalysisIntermediate
Cache eviction thrash
system-designcachingeviction - Code AnalysisIntermediate
Hot key in a cache cluster
system-designcachinghot-partition - Code AnalysisIntermediate
Consistent hashing with few vnodes
system-designconsistent-hashingload-balancing - Code AnalysisIntermediate
Deadlock from lock ordering
system-designdatabasesconcurrency - Code AnalysisIntermediate
Read-through stampede on cold start
system-designcachingstampede - Code AnalysisIntermediate
Selective column over-fetch
system-designdatabasesperformance - Code AnalysisIntermediate
Negative caching with wrong TTL
system-designcachingttl - Code AnalysisIntermediate
Double-write to cache and DB
system-designcachingcache-invalidation - Code AnalysisIntermediate
Queue with no DLQ and infinite retry
system-designmessagingdlq - Code AnalysisIntermediate
Fire-and-forget event loss
system-designmessagingoutbox - Code AnalysisIntermediate
Thundering herd from synchronized cron
system-designcachingstampede - Code AnalysisIntermediate
Cache write without invalidation on update
system-designcachingcache-invalidation - Code AnalysisIntermediate
In-memory session per instance
system-designscalabilitystateless - Code AnalysisIntermediate
Sync call in an async event loop
system-designscalabilityconcurrency - Code AnalysisIntermediate
Chatty microservice call
system-designmicroservicesperformance - Code AnalysisIntermediate
TTL jitter to prevent avalanche
cachingavalanchettl-jitter - Code AnalysisIntermediate
Connection pool exhaustion from leaked connections
connection-poolresource-leakreliability - Code AnalysisIntermediate
Unbounded cardinality metric label
metricscardinalityobservability - Code AnalysisIntermediate
Non-idempotent retry double charge
paymentsidempotencyretry - Code AnalysisIntermediate
Unbounded queue without maxsize
backpressurequeuememory - Code AnalysisIntermediate
Quorum write to minority partition
quorumpartitioncap - Code AnalysisIntermediate
Write to a read replica
replicationread-replicarouting - Code AnalysisIntermediate
Outbox relay skipped without ordering
outboxcdcordering - Code AnalysisIntermediate
Idempotent receiver dedupe check
idempotencyat-least-oncededupe - Code AnalysisIntermediate
Outbox pattern race condition
outboxexactly-oncerelay - Code AnalysisIntermediate
Kafka transaction + sink exactly-once
kafkaexactly-oncetransactions - Code AnalysisIntermediate
Redis distributed lock expiry race
distributed-lockredisfencing - Code AnalysisIntermediate
Circuit breaker half-open bug
circuit-breakerresiliencehalf-open - Code AnalysisIntermediate
Load shedding priority drop
load-sheddingadmission-controlpriority - Code AnalysisIntermediate
Cache key cardinality explosion
cachingcache-keyscardinality - Code AnalysisIntermediate
WebSocket reconnect storm
websocketreconnectthundering-herd - Code AnalysisIntermediate
Cursor pagination stability bug
paginationcursorfeed - Code AnalysisIntermediate
Non-Idempotent Payment Retry Handler
idempotencypaymentsretries - Code AnalysisIntermediate
Non-Atomic Balance Check SQL
sqlconcurrencytoctou - Code AnalysisIntermediate
At-Least-Once Consumer Duplicate Side Effect
exactly-onceconsumeridempotency - Code AnalysisIntermediate
Notification Dedup Missing TTL
notificationsdeduprace - Code AnalysisIntermediate
Feature Flag Inconsistent Rollout Seed
feature-flagsrolloutconsistency - Code AnalysisIntermediate
Tenant filter missing in query
multi-tenantisolationsql - Code AnalysisIntermediate
Unbounded tenant metric key cardinality
iotcardinalitymetrics - Code AnalysisIntermediate
Log dedup dropping distinct events
log-aggregationdedupidempotency - Code AnalysisIntermediate
A/B exposure logged after variant call
experimentationexposure-loggingbias - Code AnalysisIntermediate
Exactly-once violated by non-idempotent sink
data-pipelineexactly-onceidempotency - Code AnalysisIntermediate
JWT introspection missing signature check
identityjwtoidcsecurity - Code AnalysisIntermediate
List-objects ACL check per request
file-storageaclmetadata-db - Code AnalysisIntermediate
Violated LSP with strengthened precondition
architecturesolidlsp - Code AnalysisIntermediate
Circular dependency between modules
architecturemodularitydependencies - Code AnalysisIntermediate
Wrong abstraction: premature interface
architectureover-abstractiondi - Code AnalysisIntermediate
Coupling leak: vendor type in domain
architecturesoliddiphexagonal - Code AnalysisIntermediate
Observer memory leak
architecturedesign-patternsobserver - Code AnalysisIntermediate
Unit of Work spanning aggregates
architecturedddunit-of-work - Code AnalysisIntermediate
Strategy gone wrong: enum switch
architecturesolidocp
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