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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.
Schedule durable jobs with leases, retries and safe recovery after worker crashes.
Schedule a bounded crawl with URL deduplication, per-host politeness and crash recovery.
Generate unique IDs across workers while handling clock rollback and sequence exhaustion.
Validate a dependency graph and schedule ready work under bounded concurrency.
Coordinate leases and fencing tokens without pretending expired owners stop executing.
Run authoritative room state with ordered inputs, reconnects and ownership fencing.
Recover long-running workflows with durable history, timers and idempotent activities.
Reserve and settle long-lived resource quotas across concurrent services.
Schedule isolated build actions using complete input digests and trusted cache publication.
Design retained partition logs with fenced consumer assignments and committed offsets.
Renew and activate endpoint certificates with ownership validation and expiry visibility.
Turn released capacity into expiring waitlist offers without double allocation.
Serialize bids and deterministic closing under retries and delayed worker execution.
Form compatible game rosters while balancing skill, latency and queue wait time.
Schedule untrusted submissions behind an isolated execution boundary with versioned judging.
Assign support tickets by skills and capacity with aging, explicit ownership and reassignment.
Coordinate restaurant acceptance, preparation and courier pickup with explicit cancellation boundaries.
Coordinate atomic decisions across prepared participants with durable recovery and honest blocking semantics.
Reconcile desired resources with observed external state using generations, ownership and finalizers.
Move key ranges between owners with snapshot catch-up, enforced epochs and directory cutover.