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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.
Model spots, tickets, and pricing with clear responsibilities and safe allocation.
Design a token bucket with an injectable clock, atomic state, and useful retry hints.
Reserve seats with expiring holds and reconcile payment without overselling.
Define subscription, dispatch and error semantics for a reusable event dispatcher.
Manage bounded resources, acquisition deadlines and safe lease return under concurrency.
Coordinate producers and consumers with capacity, deadlines and explicit close semantics.
Model guarded signal phases, timed transitions and deterministic event handling.
Compose retry classification, backoff, cancellation and a total deadline.
Schedule cancellable deadlines with a min-heap, generation tokens and controlled time.
Coordinate asynchronous work with FIFO permits, cancellation and single-use release handles.
Own bounded child tasks, request cancellation on failure and join every started child.
Drive one-shot callbacks by virtual time with stable ordering, cancellation and bounded advancement.
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