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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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All types Multiple Choice Code Analysis Code

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All levels Beginner Intermediate Hard

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5,893 challenges total

Multiple ChoiceIntermediate
Strangler Fig Approach
strangler-figmigrationincremental
Multiple ChoiceHard
Avoiding Dual-Write Problems
dual-writeconsistencyanti-pattern
Multiple ChoiceHard
Saga Compensation Correctness
sagacompensationidempotency
Multiple ChoiceHard
Retry Budgets and Amplification
retry-budgetamplificationresilience
Multiple ChoiceHard
Load Shedding vs Queueing
load-sheddingoverloadbackpressure
Multiple ChoiceHard
[System Design] Cache-aside Reduce latency
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Write-through Reduce latency
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Write-behind Reduce latency
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] TTL and invalidation Reduce latency
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Cache stampede Reduce latency
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] States Fail fast for failing services
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Threshold Fail fast for failing services
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Fallback Fail fast for failing services
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Half-open test Fail fast for failing services
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Benefits Fail fast for failing services
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Command Separate read and write models
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Query Separate read and write models
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] CQRS Separate read and write models
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Materialized view Separate read and write models
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Eventual consistency Separate read and write models
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Key pattern Safe retries
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Stripe pattern Safe retries
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Idempotent HTTP Safe retries
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Duplicate detection Safe retries
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] TTL on keys Safe retries
qasys-designsys-designqa
Multiple ChoiceIntermediate
[System Design] Round robin Distribute traffic
qasys-designsys-designqa
Multiple ChoiceIntermediate
[System Design] Least connections Distribute traffic
qasys-designsys-designqa
Multiple ChoiceIntermediate
[System Design] L4 vs L7 Distribute traffic
qasys-designsys-designqa
Multiple ChoiceIntermediate
[System Design] Health check Distribute traffic
qasys-designsys-designqa
Multiple ChoiceIntermediate
[System Design] Sticky sessions Distribute traffic
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Producer/consumer Async decoupling
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] At-least-once Async decoupling
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] DLQ Async decoupling
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Kafka vs RabbitMQ Async decoupling
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Backpressure Async decoupling
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Three pillars Monitor system health
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Prometheus Monitor system health
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Grafana Monitor system health
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Distributed tracing Monitor system health
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] SLI/SLO/SLA Monitor system health
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Shard key Horizontal partition
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Range vs hash Horizontal partition
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Rebalance Horizontal partition
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Cross-shard joins Horizontal partition
qasys-designsys-designqa
Multiple ChoiceHard
[System Design] Consistent hashing Horizontal partition
qasys-designsys-designqa
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 ChoiceIntermediate
Virtual nodes in consistent hashing
system-designconsistent-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 ChoiceHard
Cache stampede / thundering herd
system-designcachingstampede
Multiple ChoiceHard
Probabilistic early expiration
system-designcachingstampede
Multiple ChoiceBeginner
Negative caching
system-designcaching
Multiple ChoiceIntermediate
TTL jitter
system-designcaching
Multiple ChoiceBeginner
CDN purpose
system-designcachingcdn
Multiple ChoiceIntermediate
CDN invalidation tradeoff
system-designcdncache-invalidation
Multiple ChoiceBeginner
Cache penetration
system-designcaching

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 — 2-minute matches, Elo ranking, and badge tiers on the line.

Coding Challenges

Strangler Fig Approach

Avoiding Dual-Write Problems

Saga Compensation Correctness

Retry Budgets and Amplification

Load Shedding vs Queueing

[System Design] Cache-aside Reduce latency

[System Design] Write-through Reduce latency

[System Design] Write-behind Reduce latency

[System Design] TTL and invalidation Reduce latency

[System Design] Cache stampede Reduce latency

[System Design] States Fail fast for failing services

[System Design] Threshold Fail fast for failing services

[System Design] Fallback Fail fast for failing services

[System Design] Half-open test Fail fast for failing services

[System Design] Benefits Fail fast for failing services

[System Design] Command Separate read and write models

[System Design] Query Separate read and write models

[System Design] CQRS Separate read and write models

[System Design] Materialized view Separate read and write models

[System Design] Eventual consistency Separate read and write models

[System Design] Key pattern Safe retries

[System Design] Stripe pattern Safe retries

[System Design] Idempotent HTTP Safe retries

[System Design] Duplicate detection Safe retries

[System Design] TTL on keys Safe retries

[System Design] Round robin Distribute traffic

[System Design] Least connections Distribute traffic

[System Design] L4 vs L7 Distribute traffic

[System Design] Health check Distribute traffic

[System Design] Sticky sessions Distribute traffic

[System Design] Producer/consumer Async decoupling

[System Design] At-least-once Async decoupling

[System Design] DLQ Async decoupling

[System Design] Kafka vs RabbitMQ Async decoupling

[System Design] Backpressure Async decoupling

[System Design] Three pillars Monitor system health

[System Design] Prometheus Monitor system health

[System Design] Grafana Monitor system health

[System Design] Distributed tracing Monitor system health

[System Design] SLI/SLO/SLA Monitor system health

[System Design] Shard key Horizontal partition

[System Design] Range vs hash Horizontal partition

[System Design] Rebalance Horizontal partition

[System Design] Cross-shard joins Horizontal partition

[System Design] Consistent hashing Horizontal partition

Stateless services and sticky sessions

Vertical vs horizontal scaling limit

L4 vs L7 load balancer

Consistent hashing vs modulo hashing

Virtual nodes in consistent hashing

Cache-aside vs write-through

Write-back cache risk

LRU vs LFU eviction

Cache stampede / thundering herd

Probabilistic early expiration

Negative caching

TTL jitter

CDN purpose

CDN invalidation tradeoff

Cache penetration

Practice now, dominate the arena