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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1,575 challenges matching your filters

Code AnalysisHard
Use-after-move of a std::string argument
use-after-movestringrvalue
Code AnalysisHard
Strict aliasing violation through reinterpret_cast
strict-aliasingreinterpret-castub
Code AnalysisHard
Uninitialized read causing sanitizer failure
uninitializedsanitizerub
Code AnalysisHard
Condition variable lost wakeup with a missing lock
condition-variableracelost-wakeup
Code AnalysisIntermediate
Missing std::forward loses value category
perfect-forwardingstd-forwardvalue-category
Code AnalysisBeginner
relaxed store load reordering output
atomicsmemory-modelcode-analysis
Code AnalysisBeginner
false sharing loop output
false-sharingperformancecode-analysis
Code AnalysisBeginner
initializer_list dangling output
initializer-listlifetimecode-analysis
Code AnalysisBeginner
const char8_t mismatch compile
char8_tunicodecode-analysis
Code AnalysisBeginner
span over temporary output
spandanglingcode-analysis
Code AnalysisBeginner
scope guard throw double output
RAIIexceptionscode-analysis
Code AnalysisIntermediate
atomic double CAS loop output
atomicsfloating-pointcode-analysis
Code AnalysisIntermediate
flat_map sort key output
flat_mapcontainerscode-analysis
Code AnalysisIntermediate
structured binding reference output
structured-bindingsrange-forcode-analysis
Code AnalysisIntermediate
pimpl unique_ptr inline dtor output
pimplunique_ptrincomplete-typecode-analysis
Code AnalysisIntermediate
to_chars buffer too small output
to_charsnumericcode-analysis
Code AnalysisHard
seqlock torn read output
seqlockdata-racecode-analysis
Code AnalysisHard
ADL swap recursion output
ADLname-lookupcode-analysis
Code AnalysisHard
friend injection capture output
friend-injectionmetaprogrammingcode-analysis
Code AnalysisHard
constexpr virtual dispatch output
constexprvirtualcode-analysis
Code AnalysisHard
dependent name template disambiguation output
two-phase-lookuptemplate-disambiguationcode-analysis
Code AnalysisBeginner
Function-Local Static Guard Output
staticmagic-staticsinit
Code AnalysisBeginner
std::atomic wait Missing Predicate
atomicwaitrace
Code AnalysisBeginner
Latch Misused as Reusable
latchreusesync
Code AnalysisBeginner
DCLP Missing Release Ordering
dclpsingletonmemory-order
Code AnalysisBeginner
union Type Punning UB
uniontype-punningub
Code AnalysisBeginner
std::function Allocation Cost
std_functionsboperformance
Code AnalysisBeginner
CRTP Static Dispatch Output
crtpstatic-dispatchtemplates
Code AnalysisBeginner
constinit with Dynamic Initializer
constinitstatic-initcompile-error
Code AnalysisIntermediate
Coroutine Frame Dangling Reference
coroutineslifetimedebugging
Code AnalysisIntermediate
Suspended Coroutine Parameter Lifetime
coroutinesframesparameters
Code AnalysisIntermediate
Barrier Completion Function Deadlock
barrierdeadlockphases
Code AnalysisIntermediate
Semaphore Release Overrun
semaphoreubcounters
Code AnalysisIntermediate
atomic_ref Misalignment
atomic_refalignmentlayout
Code AnalysisHard
Lock-Free Stack ABA Root Cause
lock-freeabacas
Code AnalysisHard
Hazard Pointer Ordering Bug
hazard-pointersmemory-orderrace
Code AnalysisHard
Static Init Order Fiasco
static-initodrtranslation-unit
Code AnalysisBeginner
initializer_list lifetime pitfall
initializer_listlifetimedangling
Code AnalysisIntermediate
void_t detection idiom SFINAE
SFINAEvoid_tdetection-idiom
Code AnalysisHard
concept subsumption ordering
conceptssubsumptionoverload-resolution
Code AnalysisIntermediate
MPMC queue index race root cause
MPMClock-freedata-race
Code AnalysisIntermediate
Dependent base member lookup
dependent-basetwo-phase-lookuptemplates
Code AnalysisBeginner
vector reallocation iterator invalidation
iterator-invalidationvectorreallocation
Code AnalysisHard
False sharing counter struct
false-sharingcache-lineperformance
Code AnalysisIntermediate
Most vexing parse snippet
most-vexing-parsesyntaxdeclaration
Code AnalysisHard
Reference dangling after vector realloc
dangling-referenceoperator[]UB
Code AnalysisHard
Broken comparator strict weak ordering
comparatorstrict-weak-orderingalgorithm
Code AnalysisBeginner
initializer_list copied in range-for
initializer_listrange-forcopy
Code AnalysisHard
noexcept move prevents copy fallback
noexceptvectorreallocation
Code AnalysisHard
Custom hash specialization misuse
hashunordered_mapspecialization
Code AnalysisIntermediate
Heterogeneous lookup necessity
heterogeneous-lookupmaptransparent-comparator
Code AnalysisBeginner
Narrowing conversion diagnostic
narrowinglist-initializationdiagnostics
Code AnalysisBeginner
Returning local by value safety
NRVOreturn-valuecopy-elision
Code AnalysisBeginner
Trace: AES-ECB Weakness
cybersecanalysisbeginner
Code AnalysisIntermediate
Trace: CORS with Credentials
cybersecanalysisintermediate
Code AnalysisHard
Trace: Predictable Token
cybersecanalysishard
Code AnalysisHard
Trace: Insecure Deserialization
cybersecanalysishard
Code AnalysisHard
Trace: Timing-Safe Compare
cybersecanalysishard
Code AnalysisIntermediate
Trace: Path Traversal
cybersecanalysisintermediate
Code AnalysisIntermediate
Trace: SQL Injection Reachability
cybersecanalysisintermediate

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

Coding Challenges

Use-after-move of a std::string argument

Strict aliasing violation through reinterpret_cast

Uninitialized read causing sanitizer failure

Condition variable lost wakeup with a missing lock

Missing std::forward loses value category

relaxed store load reordering output

false sharing loop output

initializer_list dangling output

const char8_t mismatch compile

span over temporary output

scope guard throw double output

atomic double CAS loop output

flat_map sort key output

structured binding reference output

pimpl unique_ptr inline dtor output

to_chars buffer too small output

seqlock torn read output

ADL swap recursion output

friend injection capture output

constexpr virtual dispatch output

dependent name template disambiguation output

Function-Local Static Guard Output

std::atomic wait Missing Predicate

Latch Misused as Reusable

DCLP Missing Release Ordering

union Type Punning UB

std::function Allocation Cost

CRTP Static Dispatch Output

constinit with Dynamic Initializer

Coroutine Frame Dangling Reference

Suspended Coroutine Parameter Lifetime

Barrier Completion Function Deadlock

Semaphore Release Overrun

atomic_ref Misalignment

Lock-Free Stack ABA Root Cause

Hazard Pointer Ordering Bug

Static Init Order Fiasco

initializer_list lifetime pitfall

void_t detection idiom SFINAE

concept subsumption ordering

MPMC queue index race root cause

Dependent base member lookup

vector reallocation iterator invalidation

False sharing counter struct

Most vexing parse snippet

Reference dangling after vector realloc

Broken comparator strict weak ordering

initializer_list copied in range-for

noexcept move prevents copy fallback

Custom hash specialization misuse

Heterogeneous lookup necessity

Narrowing conversion diagnostic

Returning local by value safety

Trace: AES-ECB Weakness

Trace: CORS with Credentials

Trace: Predictable Token

Trace: Insecure Deserialization

Trace: Timing-Safe Compare

Trace: Path Traversal

Trace: SQL Injection Reachability

Practice now, dominate the arena