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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.
Separate dispatch policy from car state and enforce movement safety invariants.
Build constant-time lookup and eviction with a hash map and a doubly linked list.
Model selection, payment, dispensing and refunds with guarded state transitions.
Split expenses fairly with exact money arithmetic and an auditable ledger.
Reserve seats with expiring holds and reconcile payment without overselling.
Model titles, physical copies, loans and reservations without double lending.
Compose structured logging, redaction and bounded asynchronous output.
Model a directory tree with path resolution, safe moves and consistent mutations.
Define subscription, dispatch and error semantics for a reusable event dispatcher.
Separate board rules, turn handling and game state for a testable game engine.
Model closed, open and half-open states with bounded recovery probes.
Model reversible commands, history branches and atomic grouped edits.
Allocate compatible compartments and coordinate pickup credentials with hardware outcomes.
Reserve time intervals with atomic overlap checks and explicit timezone boundaries.
Model card identity, fair shuffling and atomic dealing with injectable randomness.
Manage bounded resources, acquisition deadlines and safe lease return under concurrency.
Coordinate producers and consumers with capacity, deadlines and explicit close semantics.
Resolve object graphs with scopes, cycle detection and deterministic cleanup.
Evaluate composable discount rules with exact arithmetic and atomic redemption limits.
Compose predicates and bounded traversal without coupling query rules to storage.
Model guarded signal phases, timed transitions and deterministic event handling.
Validate a dependency graph and schedule ready work under bounded concurrency.
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