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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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188 challenges matching your filters

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Code AnalysisHard
Self-deadlock non-recursive mutex
cppthreadingmutexdeadlock
Code AnalysisBeginner
unique_lock needed for condition_variable
cppthreadingcondition-variableunique-lock
Code AnalysisBeginner
sizeof empty class
cppsizeofcode-analysis
Code AnalysisIntermediate
sizeof object with vptr
cppsizeofvtablecode-analysis
Code AnalysisHard
Lifetime extension of returned-by-value ref
cppreferenceslifetimetemporary
Code AnalysisHard
Lambda in loop capturing by reference
cpplambdacapturegotcha
Code AnalysisBeginner
Lambda capturing loop var by value
cpplambdacapturecode-analysis
Code AnalysisHard
string_view elements dangle
cppstring_viewdanglinglifetime
Code AnalysisIntermediate
constexpr used as array bound
cppconstexprarraycode-analysis
Code AnalysisHard
Header function missing inline
cppodrinlinelinker
Code AnalysisIntermediate
vector uses copy when move may throw
cppexception-safetynoexceptvector
Code AnalysisBeginner
Copy-init from derived to base object
cppobject-slicingvirtualcode-analysis
Code AnalysisIntermediate
Infinite loop optimized away
cppatomicsundefined-behavioroptimization
Code AnalysisBeginner
Use after move of string
cppmove-semanticsmoved-fromcode-analysis
Code AnalysisBeginner
Returning data() pointer of local vector
cppdanglingstlvector
Code AnalysisIntermediate
Calling empty std::function
cppstd-functioncode-analysis
Code AnalysisHard
weak_ptr use_count check is racy
cppsmart-pointersweak_ptrthread-safety
Code AnalysisHard
Forwarding reference deduction
cpptemplatesforwarding-referencecode-analysis
Code AnalysisHard
decltype(auto) vs auto
cppautodecltypetype-deduction
Code AnalysisIntermediate
No implicit void* conversion
cpptypingvoid-pointercode-analysis
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
Append to Nil Slice
code-analysisGolanguage
Code AnalysisIntermediate
Close Channel Read
code-analysisGolanguage
Code AnalysisBeginner
Copy Min
code-analysisGolanguage
Code AnalysisIntermediate
Defer LIFO
code-analysisGolanguage
Code AnalysisBeginner
For Range String
code-analysisGolanguage
Code AnalysisBeginner
Function Variable
code-analysisGolanguage
Code AnalysisHard
Goroutine Capture
code-analysisGolanguage
Code AnalysisBeginner
Interface Conversion
code-analysisGolanguage
Code AnalysisHard
Iota Math
code-analysisGolanguage
Code AnalysisBeginner
Map Comma OK
code-analysisGolanguage
Code AnalysisHard
Named Return Shadow
code-analysisGolanguage
Code AnalysisHard
Nil Interface Trap
code-analysisGolanguage
Code AnalysisBeginner
Nil Slice Len
code-analysisGolanguage
Code AnalysisHard
Panic with Defer
code-analysisGolanguage
Code AnalysisHard
Range Pointer Trap
code-analysisGolanguage
Code AnalysisBeginner
Short Var Scope
code-analysisGolanguage
Code AnalysisHard
Slice Capacity Sharing
code-analysisGolanguage
Code AnalysisBeginner
String Immutability
code-analysisGolanguage
Code AnalysisIntermediate
Switch No Expression
code-analysisGolanguage
Code AnalysisHard
Type Assert Panic
code-analysisGolanguage
Code AnalysisBeginner
Every & Some
code-analysisJavaScriptlanguage
Code AnalysisIntermediate
Async forEach
code-analysisJavaScriptlanguage
Code AnalysisBeginner
BigInt Operations
code-analysisJavaScriptlanguage
Code AnalysisIntermediate
Closure var Loop
code-analysisJavaScriptlanguage

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

Self-deadlock non-recursive mutex

unique_lock needed for condition_variable

sizeof empty class

sizeof object with vptr

Lifetime extension of returned-by-value ref

Lambda in loop capturing by reference

Lambda capturing loop var by value

string_view elements dangle

constexpr used as array bound

Header function missing inline

vector uses copy when move may throw

Copy-init from derived to base object

Infinite loop optimized away

Use after move of string

Returning data() pointer of local vector

Calling empty std::function

weak_ptr use_count check is racy

Forwarding reference deduction

decltype(auto) vs auto

No implicit void* conversion

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

Append to Nil Slice

Close Channel Read

Copy Min

Defer LIFO

For Range String

Function Variable

Goroutine Capture

Interface Conversion

Iota Math

Map Comma OK

Named Return Shadow

Nil Interface Trap

Nil Slice Len

Panic with Defer

Range Pointer Trap

Short Var Scope

Slice Capacity Sharing

String Immutability

Switch No Expression

Type Assert Panic

Every & Some

Async forEach

BigInt Operations

Closure var Loop

Practice now, dominate the arena