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Problem library
High-level architecture and low-level object design, each with progressive hints, a written analysis, approach and worked solution.
Ingest time-series data with bounded cardinality, replay and predictable query costs.
Schedule a bounded crawl with URL deduplication, per-host politeness and crash recovery.
Transform uploads into immutable variants with bounded decoding and retryable jobs.
Build a searchable index with versioned updates, secure hydration and rebuilds.
Collect tenant-scoped logs with durable ingestion, searchable indexes and retention.
Separate candidate generation, versioned ranking and real-time eligibility checks.
Track versioned automated checks, reviewer decisions and publication state.
Produce resumable authorized exports with stable snapshots and bounded resources.
Bridge a consistent snapshot to a retained change log and replay downstream safely.
Keep experiment cohorts stable and distinguish assignment from actual exposure.
Validate staged data, report row errors and commit retryable batches without silent duplication.
Collect tenant audit events with deduplication, retention and independently anchored integrity checks.
Schedule bounded analytical queries with snapshots, isolation and cancellable workers.
Coordinate authorized erasure across primary data, indexes, caches and restored backups.
Compute windowed aggregates with watermarks, late-event policy and recoverable state.
Serve versioned online features and reproduce training data without future-information leakage.
Collect linked spans with bounded buffering, sampling and explicit partial-trace results.
Track versioned dataset dependencies and answer bounded impact queries with provenance.
Count billable-like API units with deduplication, corrections and reproducible usage statements.
Derive enter/exit alerts from ordered location observations with uncertainty and hysteresis.
Count a firehose of view events and serve the most-viewed items for the last hour, day and month, fast and nearly in real time.
Serve track metadata and audio at scale while play events feed royalties and recommendations.
Answer route and ETA queries over a road graph while live traffic reports keep speeds fresh.
Rank posts by votes and age for a read-heavy front page while vote counts settle asynchronously.
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