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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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Clear topic filter- Multiple ChoiceHard
RCU Read-Side Guarantees
rcumemoryconcurrency - Multiple ChoiceHard
Lost update race
system-designconcurrencyconsistency - Multiple ChoiceHard
Optimistic vs pessimistic locking
system-designconcurrencydatabases - Code AnalysisHard
Read-modify-write lost update
system-designconcurrencydatabases - Code AnalysisHard
CAS retry livelock
system-designconcurrencydistributed-counter - Code AnalysisHard
Idempotency key stored after the effect
system-designidempotencyconcurrency - Code AnalysisHard
CAS without version on concurrent edit
system-designconcurrencydatabases - Code AnalysisHard
Lost update from read-modify-write
transactionslost-updateconcurrency - Code AnalysisHard
Idempotency: naive dedupe key
architectureidempotencyconcurrency - Code AnalysisHard
Aggregate Design for Concurrency
aggregatesconcurrencyddd
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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.