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01long sum = nums.▢ ▢ ▢ ▢02 .mapToLong(this::expensiveScore)03 .sum();
parallelStream() // nums is large AND expensiveScore is CPU-bound, stateless, side-effect-free
parallelStream() // expensiveScore writes to a shared ArrayList
parallelStream() // nums has 10 items, score is a HashMap lookup