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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2,019 challenges matching your filters

Multiple ChoiceIntermediate
Go: Select — Default Case
gointermediate
Multiple ChoiceIntermediate
Go: Select Default
gointermediate
Multiple ChoiceIntermediate
Go: sync.Mutex
gointermediate
Multiple ChoiceIntermediate
Go: sync.WaitGroup
gointermediate
Multiple ChoiceIntermediate
Go: sync.Once — Error Handling
gointermediate
Multiple ChoiceIntermediate
Go: Context — Deadline
gointermediate
Multiple ChoiceIntermediate
Go: context.WithCancel
gointermediate
Multiple ChoiceIntermediate
Go: context.WithTimeout
gointermediate
Multiple ChoiceIntermediate
Go: Embedding — Method Promotion
gointermediate
Multiple ChoiceIntermediate
Go: Promoted Methods
gointermediate
Multiple ChoiceIntermediate
Go: json.Marshal
gointermediate
Multiple ChoiceIntermediate
Go: json tags (i31)
gointermediate
Multiple ChoiceIntermediate
Go: net/http — Timeouts
gointermediate
Multiple ChoiceIntermediate
Go: http.HandleFunc
gointermediate
Multiple ChoiceIntermediate
Go: io.Reader
gointermediate
Multiple ChoiceIntermediate
Go: io.Writer
gointermediate
Multiple ChoiceIntermediate
Go: os.Open
gointermediate
Multiple ChoiceIntermediate
Go: bufio.Scanner
gointermediate
Multiple ChoiceIntermediate
Go: strconv.Itoa
gointermediate
Multiple ChoiceIntermediate
Go: strings.Contains
gointermediate
Multiple ChoiceIntermediate
Go: sort.Ints
gointermediate
Multiple ChoiceIntermediate
Go: time.Now
gointermediate
Multiple ChoiceIntermediate
Go: time.Sleep
gointermediate
Multiple ChoiceIntermediate
Go: Testing
gointermediate
Multiple ChoiceIntermediate
Go: Table Tests — Subtests
gointermediate
Multiple ChoiceIntermediate
Go: _test.go
gointermediate
Multiple ChoiceIntermediate
Go: init() — Import Order
gointermediate
Multiple ChoiceIntermediate
Go: Package Alias
gointermediate
Multiple ChoiceIntermediate
Go: Blank Import
gointermediate
Multiple ChoiceIntermediate
Go: GOPATH vs Modules
gointermediate
Multiple ChoiceIntermediate
Go: go get
gointermediate
Multiple ChoiceIntermediate
Nil Map Write
gomcqintermediate
Multiple ChoiceIntermediate
Race Detector
gomcqintermediate
Multiple ChoiceIntermediate
select default
gomcqintermediate
Multiple ChoiceIntermediate
Slice Capacity
gomcqintermediate
Multiple ChoiceIntermediate
strings.Builder
gomcqintermediate
Multiple ChoiceIntermediate
Value vs Pointer Receiver
gomcqintermediate
Multiple ChoiceIntermediate
Array splice
javascriptintermediate
Multiple ChoiceIntermediate
Array reduce
javascriptintermediate
Multiple ChoiceIntermediate
Array sort
javascriptintermediate
Multiple ChoiceIntermediate
Array flat
javascriptintermediate
Multiple ChoiceIntermediate
Array flatMap
javascriptintermediate
Multiple ChoiceIntermediate
for...in on Arrays
javascriptintermediate
Multiple ChoiceIntermediate
Array.from
javascriptintermediate
Multiple ChoiceIntermediate
Array.of
javascriptintermediate
Multiple ChoiceIntermediate
Lexical Scope
javascriptintermediate
Multiple ChoiceIntermediate
Global Scope
javascriptintermediate
Multiple ChoiceIntermediate
Closure Memory
javascriptintermediate
Multiple ChoiceIntermediate
Module Pattern
javascriptintermediate
Multiple ChoiceIntermediate
Private Variables
javascriptintermediate
Multiple ChoiceIntermediate
Class Private Fields
javascriptintermediate
Multiple ChoiceIntermediate
Closure in Event Handlers
javascriptintermediate
Multiple ChoiceIntermediate
Dynamic Scope vs Lexical
javascriptintermediate
Multiple ChoiceIntermediate
Temporal Dead Zone Revisited
javascriptintermediate
Multiple ChoiceIntermediate
Nested Closures
javascriptintermediate
Multiple ChoiceIntermediate
Once Function Pattern
javascriptintermediate
Multiple ChoiceIntermediate
Emulating Block Scope
javascriptintermediate
Multiple ChoiceIntermediate
innerHTML vs textContent
javascriptintermediate
Multiple ChoiceIntermediate
Event Bubbling
javascriptintermediate
Multiple ChoiceIntermediate
stopPropagation
javascriptintermediate

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

Go: Select — Default Case

Go: Select Default

Go: sync.Mutex

Go: sync.WaitGroup

Go: sync.Once — Error Handling

Go: Context — Deadline

Go: context.WithCancel

Go: context.WithTimeout

Go: Embedding — Method Promotion

Go: Promoted Methods

Go: json.Marshal

Go: json tags (i31)

Go: net/http — Timeouts

Go: http.HandleFunc

Go: io.Reader

Go: io.Writer

Go: os.Open

Go: bufio.Scanner

Go: strconv.Itoa

Go: strings.Contains

Go: sort.Ints

Go: time.Now

Go: time.Sleep

Go: Testing

Go: Table Tests — Subtests

Go: _test.go

Go: init() — Import Order

Go: Package Alias

Go: Blank Import

Go: GOPATH vs Modules

Go: go get

Nil Map Write

Race Detector

select default

Slice Capacity

strings.Builder

Value vs Pointer Receiver

Array splice

Array reduce

Array sort

Array flat

Array flatMap

for...in on Arrays

Array.from

Array.of

Lexical Scope

Global Scope

Closure Memory

Module Pattern

Private Variables

Class Private Fields

Closure in Event Handlers

Dynamic Scope vs Lexical

Temporal Dead Zone Revisited

Nested Closures

Once Function Pattern

Emulating Block Scope

innerHTML vs textContent

Event Bubbling

stopPropagation

Practice now, dominate the arena