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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.
Design a token bucket with an injectable clock, atomic state, and useful retry hints.
Route requests with authentication, quotas and bounded downstream failure handling.
Schedule a bounded crawl with URL deduplication, per-host politeness and crash recovery.
Enforce tenant isolation across requests, caches, jobs and resource budgets.
Design edge caching, origin protection and reliable invalidation of published content.
Protect scarce inventory with a waiting room, admission tokens and recoverable reservations.
Schedule email sends with suppression, provider feedback and honest ambiguous-outcome handling.
Reserve and settle long-lived resource quotas across concurrent services.
Schedule bounded analytical queries with snapshots, isolation and cancellable workers.
Reserve room-type inventory across every night of a stay with atomic holds and confirmation.
Count billable-like API units with deduplication, corrections and reproducible usage statements.
Merge authorized results from heterogeneous sources under bounded latency and explicit partial coverage.
Separate meeting admission, signaling and media forwarding with reconnectable participant sessions.
Fetch immutable content chunks from untrusted peers with trusted manifests and origin fallback.
Cap each client's requests across a fleet of servers without slowing every call.
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