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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.
Build a feed for millions of readers, from everyday posts to celebrity fan-out.
Deliver ordered conversations across devices, reconnects and offline recipients.
Design resumable uploads, durable metadata and secure downloads for large files.
Design partitioning, bounded staleness and stampede control for a shared cache.
Turn uploads into adaptive streams with reliable transcoding and private playback.
Ingest time-series data with bounded cardinality, replay and predictable query costs.
Maintain ordered scores with deduplicated updates, seasons and deterministic ties.
Generate unique IDs across workers while handling clock rollback and sequence exhaustion.
Transform uploads into immutable variants with bounded decoding and retryable jobs.
Create verifiable recovery points and prove they restore in an isolated environment.
Collect tenant-scoped logs with durable ingestion, searchable indexes and retention.
Define write ownership, recovery objectives and split-brain prevention across regions.
Append versioned domain events and rebuild read models without duplicating effects.
Produce resumable authorized exports with stable snapshots and bounded resources.
Implement deterministic virtual-node placement and immutable membership snapshots.
Synchronize immutable file versions with cursors, tombstones and explicit conflicts.
Publish immutable content-addressed artifacts with safe tag updates and garbage collection.
Find nearby places using spatial candidates, exact distance filtering and bounded queries.
Collect tenant audit events with deduplication, retention and independently anchored integrity checks.
Share document revisions with optimistic concurrency, resumable history and access revocation.
Manage device sessions, refresh-token rotation and bounded revocation delays.
Migrate a live dataset through snapshot backfill, ordered change capture and fenced cutover.
Evaluate bounded relationship graphs with revision-aware caching and revocation semantics.
Serve versioned online features and reproduce training data without future-information leakage.
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