Build it yourself

Small systems you implement from scratch in interviews. Grouped by pattern and tagged by role. Practise each one on LeetCode and tick it off here.

0 / 20 solved

Easy 0/3·Medium 0/13·Hard 0/4

Problem	Difficulty	Practice	Explanation	Solution
LRU cache	Medium	—	Read	—
LRU cache with TTL	Medium	—	Read	—
In-memory key-value store with nested transactions	Hard	—	Read	—

Problem	Difficulty	Practice	Explanation	Solution
Token bucket rate limiter	Easy	—	Read	—
Per-user sliding window rate limiter	Medium	—	Read	—
Retry with exponential backoff and jitter	Easy	—	Read	—
Circuit breaker	Medium	—	Read	—

Problem	Difficulty	Practice	Explanation	Solution
Worker pool with futures	Hard	—	Read	—
Delayed and recurring task scheduler	Medium	—	Read	—
Circular log buffer	Easy	—	Read	—
In-process pub/sub with topic wildcards	Medium	—	Read	—

Problem	Difficulty	Practice	Explanation	Solution
Latency percentile tracker (p50/p99)	Medium	—	Read	—
Metrics aggregator with time buckets	Medium	—	Read	—
Health checker with rise and fall thresholds	Medium	—	Read	—

Problem	Difficulty	Practice	Explanation	Solution
URL router with path parameters	Hard	—	Read	—
Consistent hashing ring	Medium	—	Read	—
Time-versioned key-value store	Medium	—	Read	—

Problem	Difficulty	Practice	Explanation	Solution
Dependency resolver with cycle detection	Medium	—	Read	—
Deep config merger with override rules	Medium	—	Read	—
Cron expression parser	Hard	—	Read	—

Must-do problem (the last-minute revision list). Company tags appear only where a public interview report names that company.

CachesEvery fast service sits behind one.0 / 3