Problems

29 problems for Backend Engineer. 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
Generate URL slugsStrings~8 minBeginner
Collect every page from an APIPagination · HTTP and REST APIs~12 minEasy
Cumulative histogram bucketsMonitoring and alerting · Statistics~10 minEasy
Exponential backoff scheduleRetries and backoff · Functions~8 minEasy
Keep the latest event per IDDictionaries · ETL pipelines~10 minEasy
Mask secrets in nested configSecurity automation · Dictionaries~12 minEasy
Read a nested value by pathJSON · Parsing text~12 minEasy
Autocomplete with a trieTries · Sorting~20 minMedium
Build an LRU cacheCaching · Classes and objects · Time and space complexity~20 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
Fetch concurrently with a limitasyncio · Threads and concurrency~20 minMedium
p95 latency per routeLog analysis · Statistics · Parsing text~20 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
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
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
Exactly-once effects over at-least-once deliverySimulation and state machines · Hashing · ETL pipelines~45 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