easyArrays & Hashing
Event Frequency Ledger
Summarize repeated event codes for a telemetry batch.
Practice challengeCodeArena challenge library
120 challenges match your filters.
easyArrays & Hashing
Scholarship Tag Counter
Count normalized scholarship tags for discovery ranking.
Practice challengemediumArrays & Hashing
Inventory Signal Index
Build a stable count index for marketplace inventory signals.
Practice challengehardArrays & Hashing
Assessment Answer Histogram
Count answer choices without losing case-sensitive distinctions.
Practice challengeeasyArrays & Hashing
Application Fee Pair
Find the earliest two fees that exactly match a budget.
Practice challengeeasyArrays & Hashing
Capacity Pair Finder
Locate the first compatible capacity pair for a deployment target.
Practice challengemediumArrays & Hashing
Course Credit Pair
Find two course-credit values that reach a graduation requirement.
Practice challengehardArrays & Hashing
Travel Cost Pair
Find two quoted costs that use the remaining travel allowance.
Practice challengeeasyArrays & Hashing
Deadline Interval Merge
Normalize overlapping admissions deadline windows.
Practice challengeeasyArrays & Hashing
Maintenance Window Merge
Merge overlapping platform maintenance periods.
Practice challengemediumArrays & Hashing
Interview Availability Merge
Consolidate overlapping interview availability blocks.
Practice challengehardArrays & Hashing
Visa Appointment Window Merge
Canonicalize overlapping appointment windows.
Practice challengeeasyStrings & Parsing
Program Route Canonicalizer
Convert a program title into a safe deterministic route slug.
Practice challengeeasyStrings & Parsing
Institution Slug Builder
Normalize an institution name for public URLs.
Practice challengemediumStrings & Parsing
Evidence Label Canonicalizer
Create stable labels for uploaded evidence categories.
Practice challengehardStrings & Parsing
Community Topic Slug
Normalize a community topic without duplicate separators.
Practice challengeeasyStrings & Parsing
Scholarship Name Matcher
Match scholarship names against ? and * search patterns.
Practice challengeeasyStrings & Parsing
Log Route Matcher
Match normalized request paths against a wildcard policy.
Practice challengemediumStrings & Parsing
Course Catalog Matcher
Evaluate a catalog title against a constrained wildcard query.
Practice challengehardStrings & Parsing
File Policy Matcher
Match a safe filename against a policy expression.
Practice challengeeasyStrings & Parsing
Essay Phrase Families
Group phrases that contain the same letters after case normalization.
Practice challengeeasyStrings & Parsing
Program Code Families
Group program codes that are anagrams under normalization.
Practice challengemediumStrings & Parsing
Interview Token Families
Cluster interview tokens by canonical character signature.
Practice challengehardStrings & Parsing
Domain Alias Families
Group alias labels with the same normalized letters.
Practice challengeeasyStacks & Queues
Application Template Balance
Validate nested placeholders in an application template.
Practice challengeeasyStacks & Queues
Policy Expression Balance
Check mixed delimiters in a policy expression.
Practice challengemediumStacks & Queues
Markdown Component Balance
Validate nested component markers before rendering.
Practice challengehardStacks & Queues
Configuration Nesting Audit
Measure balanced configuration nesting depth.
Practice challengeeasyStacks & Queues
Score Formula Evaluator
Evaluate a postfix assessment-scoring expression.
Practice challengeeasyStacks & Queues
Budget Formula Evaluator
Compute a postfix funding formula with integer arithmetic.
Practice challengemediumStacks & Queues
Quota Formula Evaluator
Evaluate a compact postfix quota expression.
Practice challengehardStacks & Queues
Capacity Formula Evaluator
Compute a postfix capacity estimate.
Practice challengeeasyStacks & Queues
Next Higher Score
Find the next higher assessment score to the right.
Practice challengeeasyStacks & Queues
Next Larger Queue Depth
Find the next larger worker backlog observation.
Practice challengemediumStacks & Queues
Next Higher Tuition Quote
Find the next higher tuition quote in a sequence.
Practice challengehardStacks & Queues
Next Greater Latency
Find the first later latency that is strictly larger.
Practice challengeeasyTrees & Graphs
Campus Transfer Hops
Find the fewest transfer hops between two campus locations.
Practice challengeeasyTrees & Graphs
Learning Path Hops
Find the shortest prerequisite connection between two skills.
Practice challengemediumTrees & Graphs
Support Escalation Hops
Measure the shortest escalation path in a support graph.
Practice challengehardTrees & Graphs
Regional Routing Hops
Find the minimum routing hops between service regions.
Practice challengeeasyTrees & Graphs
Course Dependency Order
Produce a stable course completion order.
Practice challengeeasyTrees & Graphs
Deployment Stage Order
Order deployment stages from prerequisite edges.
Practice challengemediumTrees & Graphs
Document Workflow Order
Resolve a deterministic document-processing sequence.
Practice challengehardTrees & Graphs
Certification Topic Order
Order certification topics or reject a cycle.
Practice challengeeasyTrees & Graphs
Learner Cohort Components
Group learners connected by collaboration edges.
Practice challengeeasyTrees & Graphs
Service Dependency Components
Identify disconnected service dependency groups.
Practice challengemediumTrees & Graphs
Institution Network Components
Group institutions connected by exchange agreements.
Practice challengehardTrees & Graphs
Incident Blast Components
Find connected components in an incident dependency graph.
Practice challengeeasyDynamic Programming
Fee Denomination Planner
Minimize the number of allowed fee units needed for an exact total.
Practice challengeeasyDynamic Programming
Study Credit Planner
Reach an exact credit target with the fewest reusable modules.
Practice challengemediumDynamic Programming
Voucher Composition
Compose an exact voucher amount with the fewest denominations.
Practice challengehardDynamic Programming
Compute Credit Allocation
Reach a compute-credit target with the fewest pack sizes.
Practice challengeeasyDynamic Programming
Program Name Distance
Measure edit distance between two program names.
Practice challengeeasyDynamic Programming
Transcript Label Distance
Measure correction distance between transcript labels.
Practice challengemediumDynamic Programming
Skill Name Distance
Compute the edit distance between skill identifiers.
Practice challengehardDynamic Programming
Institution Alias Distance
Measure normalization effort between institution aliases.
Practice challengeeasyDynamic Programming
Progression Signal
Find the longest strictly increasing assessment progression.
Practice challengeeasyDynamic Programming
Capacity Growth Sequence
Find the longest strictly increasing capacity subsequence.
Practice challengemediumDynamic Programming
Scholarship Improvement Run
Measure the longest increasing funding-offer sequence.
Practice challengehardDynamic Programming
Latency Regression Sequence
Find the longest strictly increasing latency subsequence.
Practice challengeeasyDebugging & Testing
Inclusive Age Band Repair
Fix an off-by-one age-band filter.
Practice challengeeasyDebugging & Testing
Score Threshold Repair
Retain scores at both inclusive threshold boundaries.
Practice challengemediumDebugging & Testing
Date Window Boundary Repair
Correct inclusive date-window selection.
Practice challengehardDebugging & Testing
Inventory Limit Repair
Preserve values exactly at stock-policy limits.
Practice challengeeasyDebugging & Testing
Content Review State Machine
Replay content-review transitions and stop on an illegal move.
Practice challengeeasyDebugging & Testing
Application State Machine
Validate an application lifecycle transition sequence.
Practice challengemediumDebugging & Testing
Order State Machine
Replay order states with strict transition rules.
Practice challengehardDebugging & Testing
Incident State Machine
Validate incident response state changes.
Practice challengeeasyDebugging & Testing
Authorization Test Gap
List authorization branches missing from the test plan.
Practice challengeeasyDebugging & Testing
Payment Test Gap
Find uncovered payment decision branches.
Practice challengemediumDebugging & Testing
Mobile Navigation Test Gap
Identify mobile-navigation branches lacking coverage.
Practice challengehardDebugging & Testing
Runner Security Test Gap
List untested code-runner security outcomes.
Practice challengeeasyBackend & APIs
Payment Idempotency Ledger
Classify repeated payment requests by key and payload identity.
Practice challengeeasyBackend & APIs
Enrollment Idempotency Ledger
Prevent duplicate enrollments while detecting key conflicts.
Practice challengemediumBackend & APIs
Webhook Idempotency Ledger
Classify repeated webhook deliveries safely.
Practice challengehardBackend & APIs
Document Upload Idempotency
Prevent duplicate document writes under retries.
Practice challengeeasyBackend & APIs
Application Cursor Page
Page applications by created time and stable identifier.
Practice challengeeasyBackend & APIs
Course Cursor Page
Return a stable cursor page of courses.
Practice challengemediumBackend & APIs
Order Cursor Page
Page seller orders without offset drift.
Practice challengehardBackend & APIs
Message Cursor Page
Return a stable page of messages.
Practice challengeeasyBackend & APIs
API Sliding Window
Apply a sliding-window API request limit.
Practice challengeeasyBackend & APIs
Login Attempt Window
Evaluate login attempts against a sliding policy.
Practice challengemediumBackend & APIs
Submission Rate Window
Apply a coding-submission rate limit.
Practice challengehardBackend & APIs
Email Dispatch Window
Evaluate email dispatch requests under a rolling quota.
Practice challengeeasyCloud & DevOps
Pod Placement Decision
Choose a node that satisfies CPU, memory, and label constraints.
Practice challengeeasyCloud & DevOps
Runner Placement Decision
Schedule a runner onto an eligible isolated node.
Practice challengemediumCloud & DevOps
Worker Placement Decision
Select a node for a background worker.
Practice challengehardCloud & DevOps
Scanner Placement Decision
Place a malware scanner using deterministic capacity rules.
Practice challengeeasyCloud & DevOps
Deployment Availability Gate
Decide whether a rolling deployment may continue.
Practice challengeeasyCloud & DevOps
Runner Upgrade Gate
Evaluate availability before advancing a runner rollout.
Practice challengemediumCloud & DevOps
Database Proxy Rollout Gate
Check whether proxy rollout can proceed.
Practice challengehardCloud & DevOps
Search Worker Rollout Gate
Evaluate a worker deployment against max-unavailable.
Practice challengeeasyCloud & DevOps
Database Backup RPO
Check observed database backup gaps against RPO.
Practice challengeeasyCloud & DevOps
Object Store Backup RPO
Evaluate protected-object backup timing.
Practice challengemediumCloud & DevOps
Audit Archive RPO
Measure audit-archive backup compliance.
Practice challengehardCloud & DevOps
Source Registry Backup RPO
Check official-source registry backup gaps.
Practice challengeeasySecure Coding
Support Log Redactor
Remove emails, card-like numbers, and named secrets from support logs.
Practice challengeeasySecure Coding
Runner Log Redactor
Redact sensitive patterns from code-runner diagnostics.
Practice challengemediumSecure Coding
Application Note Redactor
Remove contact and secret material from operational notes.
Practice challengehardSecure Coding
Webhook Error Redactor
Redact sensitive values before webhook errors are persisted.
Practice challengeeasySecure Coding
Scholarship Source Allowlist
Validate a scholarship URL against an official-host allowlist.
Practice challengeeasySecure Coding
Runner Callback Allowlist
Validate a runner callback target.
Practice challengemediumSecure Coding
Document Fetch Allowlist
Validate a remote document source without private-network access.
Practice challengehardSecure Coding
Institution API Allowlist
Validate an institutional API endpoint.
Practice challengeeasySecure Coding
Marketplace Permission Decision
Evaluate deny-overrides marketplace permissions.
Practice challengeeasySecure Coding
Admissions Permission Decision
Evaluate admissions workspace authorization rules.
Practice challengemediumSecure Coding
Family Permission Decision
Evaluate guardian and child resource permissions.
Practice challengehardSecure Coding
Runner Permission Decision
Evaluate runner operations under deny-overrides policy.
Practice challengeeasySystem Design
Credential Ledger Quorum
Evaluate credential-ledger quorum availability and overlap.
Practice challengeeasySystem Design
Application Store Quorum
Evaluate application-store read/write quorums.
Practice challengemediumSystem Design
Progress Store Quorum
Assess learning-progress quorum behavior.
Practice challengehardSystem Design
Order Ledger Quorum
Evaluate order-ledger quorum guarantees.
Practice challengeeasySystem Design
Learner Shard Assignment
Assign a learner key to a stable shard.
Practice challengeeasySystem Design
Institution Shard Assignment
Map an institution key to a data shard.
Practice challengemediumSystem Design
Submission Shard Assignment
Assign a submission key deterministically.
Practice challengehardSystem Design
Tenant Shard Assignment
Map a tenant key using the documented hash rule.
Practice challengeeasySystem Design
Exam Traffic Capacity
Estimate required instances for peak exam traffic.
Practice challengeeasySystem Design
Code Runner Capacity
Estimate runner-control-plane instance capacity.
Practice challengemediumSystem Design
Application Deadline Capacity
Size services for an admissions deadline spike.
Practice challengehardSystem Design
Marketplace Campaign Capacity
Estimate instances for campaign peak load.
Practice challenge