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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All types Multiple Choice Code Analysis Code

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All levels Beginner Intermediate Hard

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63 challenges matching your filters

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Code AnalysisHard
Array Decay
code-analysisClanguage
Code AnalysisHard
Const Cast
code-analysisClanguage
Code AnalysisHard
Dangling Pointer
code-analysisClanguage
Code AnalysisHard
Negative Modulo
code-analysisClanguage
Code AnalysisHard
restrict Pointer
code-analysisClanguage
Code AnalysisHard
Shift Overflow
code-analysisClanguage
Code AnalysisHard
Struct Sizeof
code-analysisClanguage
Code AnalysisHard
Switch Fall-through
code-analysisClanguage
Code AnalysisHard
Type Promotion
code-analysisClanguage
Code AnalysisHard
Unsigned Underflow
code-analysisClanguage
Code AnalysisHard
XOR Swap Same
code-analysisClanguage
Code AnalysisHard
Dangling string_view from temporary
cppstring_viewdanglingcode-analysis
Code AnalysisHard
Pessimizing std::move on return
cppmove-semanticsrvoanti-pattern
Code AnalysisHard
shared_ptr reference cycle
cppsmart-pointersshared_ptrmemory-leak
Code AnalysisHard
Cross-TU static init order
cppstatic-initodrundefined-behavior
Code AnalysisHard
Lifetime extension of temporary subobject binding
cppreferenceslifetimetemporary
Code AnalysisHard
Missing std::forward loses rvalueness
cpptemplatesperfect-forwardingstd-forward
Code AnalysisHard
Exception-unsafe member update
cppexception-safetycode-analysis
Code AnalysisHard
static_cast vs dynamic_cast downcast
cppcastingundefined-behaviorcode-analysis
Code AnalysisHard
Relaxed store publish bug
cppatomicsmemory-ordercode-analysis
Code AnalysisHard
initializer_list in emplace_back
cppstlemplacebraced-init
Code AnalysisHard
Self-deadlock non-recursive mutex
cppthreadingmutexdeadlock
Code AnalysisHard
Lifetime extension of returned-by-value ref
cppreferenceslifetimetemporary
Code AnalysisHard
Lambda in loop capturing by reference
cpplambdacapturegotcha
Code AnalysisHard
string_view elements dangle
cppstring_viewdanglinglifetime
Code AnalysisHard
Header function missing inline
cppodrinlinelinker
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 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 AnalysisHard
Goroutine Capture
code-analysisGolanguage
Code AnalysisHard
Iota Math
code-analysisGolanguage
Code AnalysisHard
Named Return Shadow
code-analysisGolanguage
Code AnalysisHard
Nil Interface Trap
code-analysisGolanguage
Code AnalysisHard
Panic with Defer
code-analysisGolanguage
Code AnalysisHard
Range Pointer Trap
code-analysisGolanguage
Code AnalysisHard
Slice Capacity Sharing
code-analysisGolanguage
Code AnalysisHard
Type Assert Panic
code-analysisGolanguage
Code AnalysisHard
IIFE Semicolon Trap
code-analysisJavaScriptlanguage
Code AnalysisHard
Proxy Trap
code-analysisJavaScriptlanguage
Code AnalysisHard
Sparse Array
code-analysisJavaScriptlanguage
Code AnalysisHard
String Coercion
code-analysisJavaScriptlanguage
Code AnalysisHard
Type Coercion Madness
code-analysisJavaScriptlanguage
Code AnalysisHard
Class Variable Shadow
code-analysisPythonlanguage
Code AnalysisHard
Decorator Order
code-analysisPythonlanguage
Code AnalysisHard
is vs == (int cache)
code-analysisPythonlanguage
Code AnalysisHard
Multiple Inheritance MRO
code-analysisPythonlanguage
Code AnalysisHard
Mutable Default Arg
code-analysisPythonlanguage
Code AnalysisHard
String Interning
code-analysisPythonlanguage
Code AnalysisHard
Walrus in Comprehension
code-analysisPythonlanguage
Code AnalysisHard
Violated principle in subclass override
lspsolidcode-analysis
Code AnalysisHard
Wrong abstraction refactor
wrong-abstractionrefactoringcode-analysis
Code AnalysisHard
CRDT operation design
crdtcollaborative-editingcode-analysis
Code AnalysisHard
Rules engine vs hard-coded conditions
rules-enginedecision-tablescode-analysis
Code AnalysisHard
Which Failure Mode FMEA
fmeafailure-modestimeoutscode-analysis
Code AnalysisHard
Which Security Boundary Gap
zero-trustsecurity-architecturecode-analysis

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

Array Decay

Const Cast

Dangling Pointer

Negative Modulo

restrict Pointer

Shift Overflow

Struct Sizeof

Switch Fall-through

Type Promotion

Unsigned Underflow

XOR Swap Same

Dangling string_view from temporary

Pessimizing std::move on return

shared_ptr reference cycle

Cross-TU static init order

Lifetime extension of temporary subobject binding

Missing std::forward loses rvalueness

Exception-unsafe member update

static_cast vs dynamic_cast downcast

Relaxed store publish bug

initializer_list in emplace_back

Self-deadlock non-recursive mutex

Lifetime extension of returned-by-value ref

Lambda in loop capturing by reference

string_view elements dangle

Header function missing inline

weak_ptr use_count check is racy

Forwarding reference deduction

decltype(auto) vs auto

seqlock torn read output

ADL swap recursion output

friend injection capture output

constexpr virtual dispatch output

dependent name template disambiguation output

Goroutine Capture

Iota Math

Named Return Shadow

Nil Interface Trap

Panic with Defer

Range Pointer Trap

Slice Capacity Sharing

Type Assert Panic

IIFE Semicolon Trap

Proxy Trap

Sparse Array

String Coercion

Type Coercion Madness

Class Variable Shadow

Decorator Order

is vs == (int cache)

Multiple Inheritance MRO

Mutable Default Arg

String Interning

Walrus in Comprehension

Violated principle in subclass override

Wrong abstraction refactor

CRDT operation design

Rules engine vs hard-coded conditions

Which Failure Mode FMEA

Which Security Boundary Gap

Practice now, dominate the arena