Start by clarifying the problem and constraints, then outline a level-synchronous BFS where each thread processes a disjoint subset of the current frontier. Explain how to use thread-safe data structures and synchronization to maintain level ordering and avoid duplicate work, and discuss trade-offs like contention, memory overhead, and determinism.
Pro tip: Emphasize that the visited set must be updated atomically during neighbor expansion to prevent duplicate enqueues, and consider using a concurrent hash set with fine-grained locking or lock-free operations to minimize contention.
Restate the rotating-lock problem (e.g., shortest sequence of rotations to reach target) and confirm assumptions like state space size, thread count, and whether determinism is required.
Explain that BFS processes level by level; parallelize by splitting the current frontier among threads, with a barrier after each level to maintain ordering.
Use a concurrent queue for the next frontier and a thread-safe visited set (e.g., ConcurrentHashMap or lock-free set) with atomic check-and-set to avoid duplicate exploration.
Discuss partitioning work to reduce contention, using per-thread local queues merged at barriers, and minimizing lock granularity.
Weigh contention vs. parallelism, memory overhead of visited set and queues, and determinism (order of exploration may vary but shortest path length remains correct).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.