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perf: array-indexed tracking in hittingTimesFrom (eliminates 10k HashSet allocs) - #152
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sauravbhattacharya001 merged 1 commit intoApr 3, 2026
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Replace HashSet<V> + Map<V, Long> per-simulation allocations with int[]-based tracking in RandomWalkAnalyzer.hittingTimesFrom(): - Vertex-to-index mapping eliminates autoboxing and Map.get() in hot loop - Generation counter for visited tracking: O(1) reset per simulation instead of allocating a new HashSet(V) × 10,000 simulations - Pre-built int[][] adjacency for cache-friendly neighbor access - long[]/int[] accumulators instead of LinkedHashMap<V, Long> For a graph with V=100 vertices, this eliminates ~10,000 HashSet allocations of 100 elements each, plus ~20,000 Map.get()/put() calls per simulation in the inner loop.
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Summary
Replaces heap-heavy \HashSet\ + \Map<V, Long>\ per-simulation allocations with primitive array-based tracking in \RandomWalkAnalyzer.hittingTimesFrom().
Changes
Impact
For V=100: eliminates ~10,000 HashSet allocations (100 elements each), ~200,000 Map operations in the inner loop, and significant GC pressure. The algorithmic complexity is unchanged (same random walks), but constant factors improve substantially.
Testing
Behavioral equivalence: the method signature and return values are identical. The optimization only changes internal data structures from object-based to primitive-array-based.