Problems

100 problems. Read any of them; sign in to code, run and submit.

Classify request latenciesLoops and control flow · Lists and tuples~5 minBeginner
Count HTTP status classesDictionaries · Monitoring and alerting~5 minBeginner
Count ready podsKubernetes · Strings~6 minBeginner
Count unique client IPsSets · Log analysis · Strings~6 minBeginner
Count word frequenciesStrings · Dictionaries~8 minBeginner
Disk usage by top-level directoryDictionaries · Strings · Files and configuration~8 minBeginner
Flatten nested batchesLists and tuples · Loops and control flow~5 minBeginner
Format bytes for humansFormatting output · Functions~8 minBeginner
Generate URL slugsStrings~8 minBeginner
Leaderboard top NSorting · Lists and tuples~7 minBeginner
Merge resource tagsDictionaries~6 minBeginner
Normalise and deduplicate hostnamesStrings · Lists and tuples · Sets~8 minBeginner
Parse a .env fileFiles and configuration · Strings · Dictionaries~10 minBeginner
Reverse the word orderStrings · Lists and tuples~5 minBeginner
Running averageLoops and control flow · Statistics~6 minBeginner
Split work into batchesLists and tuples · Loops and control flow~5 minBeginner
Summarise service statusesDictionaries · Loops and control flow~6 minBeginner
Summarise test resultsTesting and test data · Dictionaries~7 minBeginner
Transpose a metrics tableLists and tuples~5 minBeginner
Validate environment variable namesStrings · Validation and schemas~6 minBeginner
Check balanced brackets in a templateStacks and queues · Strings~10 minEasy
Collect every page from an APIPagination · HTTP and REST APIs~12 minEasy
Cosine similarity of embeddingsVectors and embeddings · Functions~8 minEasy
Count log levelsLog analysis · Parsing text~10 minEasy
Cumulative histogram bucketsMonitoring and alerting · Statistics~10 minEasy
Detect flaky testsTesting and test data · Dictionaries~10 minEasy
Diff two configurationsDictionaries · Infrastructure as code~10 minEasy
Expand a cron fieldParsing text · Dates and times~15 minEasy
Exponential backoff scheduleRetries and backoff · Functions~8 minEasy
Group anagramsHashing · Dictionaries · Sorting~10 minEasy
Group-by aggregationSQL patterns in Python · ETL pipelines · Dictionaries~12 minEasy
Keep the latest event per IDDictionaries · ETL pipelines~10 minEasy
Latest model version per stageDictionaries · Model evaluation~10 minEasy
List actions an IAM policy allowsIAM and policies · AWS SDK (Boto3-style) · JSON~12 minEasy
Mask secrets in nested configSecurity automation · Dictionaries~12 minEasy
Parse a CSV export into typed recordsETL pipelines · Parsing text~12 minEasy
Parse an AWS ARNAWS SDK (Boto3-style) · Parsing text · Strings~10 minEasy
Parse INI sectionsFiles and configuration · Parsing text · Dictionaries~12 minEasy
Plan log file rotationFiles and configuration · Lists and tuples~12 minEasy
Read a nested value by pathJSON · Parsing text~12 minEasy
Render a prompt templateLLM integration · Strings · Regular expressions~12 minEasy
Size S3 prefixesAWS SDK (Boto3-style) · Dictionaries · Strings~10 minEasy
Sort semantic versionsSorting · Parsing text~12 minEasy
Tokenise text for an LLM pipelineLLM integration · Strings · Regular expressions~10 minEasy
Total Kubernetes resource requestsKubernetes · Parsing text~15 minEasy
Alert on error-rate windowsMonitoring and alerting · Intervals · Simulation and state machines~25 minMedium
Autocomplete with a trieTries · Sorting~20 minMedium
Build a lazy generator pipelineGenerators and laziness · Time and space complexity~20 minMedium
Build an LRU cacheCaching · Classes and objects · Time and space complexity~20 minMedium
Chunk documents with overlap for RAGRetrieval-augmented generation · Lists and tuples · LLM integration~15 minMedium
Clean a JSON Lines exportETL pipelines · JSON · Validation and schemas~20 minMedium
Compute an invoice with dataclassesDataclasses · Classes and objects · Formatting output~20 minMedium
Decide whether to promote a canaryMonitoring and alerting · Statistics~20 minMedium
Fall back to a second model on timeoutasyncio · Resilience patterns · LLM integration~20 minMedium
Fetch concurrently with a limitasyncio · Threads and concurrency~20 minMedium
Find idle EC2 instancesAWS SDK (Boto3-style) · Pagination~20 minMedium
Find the first bad buildBinary search · Time and space complexity~15 minMedium
Keyword retrieval with TF-IDFRetrieval-augmented generation · Statistics · Dictionaries~25 minMedium
Lowest-latency route between servicesGraphs · Heaps~25 minMedium
Merge maintenance windowsIntervals · Sorting~15 minMedium
Most frequent errors in a streamHeaps · Hashing · Generators and laziness~15 minMedium
Order deployments by dependencyGraphs · Sorting~20 minMedium
p95 latency per routeLog analysis · Statistics · Parsing text~20 minMedium
Plan an S3 cleanup in batchesAWS SDK (Boto3-style) · Pagination · Lists and tuples~20 minMedium
Plan changes from desired stateInfrastructure as code · Dictionaries~20 minMedium
Repair structured output from an LLMLLM integration · JSON · Parsing text~20 minMedium
Report unhealthy podsKubernetes · JSON · Monitoring and alerting~20 minMedium
Resolve variable referencesFiles and configuration · Graphs · Parsing text~20 minMedium
Run health checks in parallel threadsThreads and concurrency · Exceptions~20 minMedium
Scale features for a modelStatistics · Vectors and embeddings · Lists and tuples~15 minMedium
Summarise a Terraform planInfrastructure as code · JSON~15 minMedium
Time code with a context managerContext managers · Classes and objects · Exceptions~15 minMedium
Token bucket rate limiterRate limiting · Simulation and state machines~20 minMedium
Validate a request against a schemaValidation and schemas · JSON~25 minMedium
Write a retry decoratorDecorators · Retries and backoff · Exceptions~20 minMedium
Async worker pool with retriesasyncio · Retries and backoff · Threads and concurrency~30 minHard
Compute the next cron runDates and times · Parsing text · Simulation and state machines~40 minHard
Detect latency anomalies with z-scoresStatistics · Monitoring and alerting · Time and space complexity~25 minHard
Diversify retrieval with MMRRetrieval-augmented generation · Vectors and embeddings~30 minHard
Fit a conversation into a token budgetLLM integration · Time and space complexity~30 minHard
Implement a circuit breakerResilience patterns · Simulation and state machines · Classes and objects~30 minHard
Parse a server-sent event streamStreaming responses · Parsing text · Generators and laziness~30 minHard
Partition keys with a consistent hash ringHashing · Binary search~30 minHard
Plan multi-region trafficResilience patterns · Sorting · Simulation and state machines~30 minHard
Plan server capacity at minimum costDynamic programming · Time and space complexity~40 minHard
Precision, recall and F1Model evaluation · Statistics~25 minHard
Report vulnerable dependenciesSecurity automation · Parsing text · Sorting~30 minHard
Resolve package versionsGraphs · Parsing text · Sorting~40 minHard
Scan code for leaked secretsSecurity automation · Regular expressions · Statistics~30 minHard
Simulate a Kubernetes rolling updateKubernetes · Simulation and state machines~30 minHard
Sync through a rate-limited APIRate limiting · Retries and backoff · Pagination~35 minHard
Window functions in PythonSQL patterns in Python · Sorting · ETL pipelines~30 minHard
Advance a Raft leader's commit indexSimulation and state machines · Sorting~45 minExpert
Build a resilient LLM gatewayResilience patterns · Retries and backoff · LLM integration~60 minExpert
Exactly-once effects over at-least-once deliverySimulation and state machines · Hashing · ETL pipelines~45 minExpert
Orchestrate an agent's tool planAI agents and tools · Graphs · Retries and backoff~60 minExpert
Order events with vector clocksSimulation and state machines · Dictionaries~40 minExpert
Route MCP tool calls over JSON-RPCMCP and JSON-RPC · Validation and schemas · JSON~60 minExpert
Simulate the Horizontal Pod AutoscalerKubernetes · Simulation and state machines · Monitoring and alerting~45 minExpert
Weighted fair-share job schedulerHeaps · Simulation and state machines~60 minExpert