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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.
Separate dispatch policy from car state and enforce movement safety invariants.
Split expenses fairly with exact money arithmetic and an auditable ledger.
Separate board rules, turn handling and game state for a testable game engine.
Reserve time intervals with atomic overlap checks and explicit timezone boundaries.
Compose predicates and bounded traversal without coupling query rules to storage.
Validate a dependency graph and schedule ready work under bounded concurrency.
Tokenize and parse arithmetic with precedence, unary operators and bounded evaluation.
Build a bounded probabilistic membership structure with compatible serialization.
Maintain conflict-free half-open reservations with atomic rescheduling.
Track connected components with path compression, union by size and stable API rules.
Find overlapping intervals using an augmented balanced search tree.
Solve bounded 9×9 boards with candidate masks, backtracking and explicit uniqueness status.
Produce deterministic minimal insertion/deletion scripts and apply them against a verified base.
Find shortest paths on immutable directed graphs with nonnegative integer weights.
Sample immutable integer weights using prefix sums and an injectable unbiased draw source.
Find strongly connected components and produce an acyclic condensation graph.
Find overlapping byte-pattern occurrences across chunks using a prefix-function automaton.
Match scalar strings with literal tokens, question marks and stars using bounded dynamic programming.
Track exact extrema for the most recent k samples using monotonic deques.
Clone a restricted data graph while preserving cycles and shared references without invoking accessors.
Compute exact integer maximum flow with residual reverse edges and a minimum-cut certificate.
Recompute affected formula cells through a validated dependency graph with explicit cycle and error semantics.
Count a firehose of view events and serve the most-viewed items for the last hour, day and month, fast and nearly in real time.
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