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.
Filter by type
Filter by difficulty
Popular topics
702 challenges matching your filters
- Code AnalysisIntermediate
constexpr used as array bound
cppconstexprarraycode-analysis - Code AnalysisIntermediate
vector uses copy when move may throw
cppexception-safetynoexceptvector - Code AnalysisIntermediate
Infinite loop optimized away
cppatomicsundefined-behavioroptimization - Code AnalysisIntermediate
Calling empty std::function
cppstd-functioncode-analysis - Code AnalysisIntermediate
No implicit void* conversion
cpptypingvoid-pointercode-analysis - Code AnalysisIntermediate
Iterator invalidation while erasing in a vector loop
iterator-invalidationvectorerase - Code AnalysisIntermediate
Dangling pointer to a local vector's data
dangling-pointervectorlifetime - Code AnalysisIntermediate
Attempting to copy a unique_ptr
unique-ptrmove-onlycompile-error - Code AnalysisIntermediate
Cross-thread visibility with a relaxed flag
memory-orderatomicsdata-race - Code AnalysisIntermediate
Self-deadlock from locking a non-recursive mutex twice
deadlockmutexconcurrency - Code AnalysisIntermediate
Missing std::forward loses value category
perfect-forwardingstd-forwardvalue-category - 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 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 AnalysisIntermediate
void_t detection idiom SFINAE
SFINAEvoid_tdetection-idiom - Code AnalysisIntermediate
MPMC queue index race root cause
MPMClock-freedata-race - Code AnalysisIntermediate
Dependent base member lookup
dependent-basetwo-phase-lookuptemplates - Code AnalysisIntermediate
Most vexing parse snippet
most-vexing-parsesyntaxdeclaration - Code AnalysisIntermediate
Heterogeneous lookup necessity
heterogeneous-lookupmaptransparent-comparator - Code AnalysisIntermediate
Trace: CORS with Credentials
cybersecanalysisintermediate - Code AnalysisIntermediate
Trace: Path Traversal
cybersecanalysisintermediate - Code AnalysisIntermediate
Trace: SQL Injection Reachability
cybersecanalysisintermediate - Code AnalysisIntermediate
Trace: Memoized Fibonacci
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Sliding Window Max Sum
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Balanced Parentheses
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Concat Merge
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Fill Method
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Array Flat
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Array.from
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Join to String
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: LastIndexOf
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Reverse In-Place
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Shift Operation
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Default Sort
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Splice Remove
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Unshift Operation
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Loose Equality
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: String Coercion
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Strict Equality
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Date Difference
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Date Epoch
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Array Destructure
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: JSON Clone Limits
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: JSON Reviver
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Map Iteration
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Map Operations
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Math.abs
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Math.ceil
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Math.floor
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Math.round
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Number Conversion
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: ParseFloat
dsaanalysisintermediate - Code AnalysisIntermediate
Trace: Rest Parameters
dsaanalysisintermediate
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.