用Collect处理素数问题

最新推荐文章于 2025-11-26 03:49:59 发布

翻译最新推荐文章于 2025-11-26 03:49:59 发布 · 144 阅读

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#stream #lambda

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public class PrimeNumbersCollector implements java.util.stream.Collector<Integer, Map<Boolean, List<Integer>>, Map<Boolean, List<Integer>>> {
    @Override
    public Supplier<Map<Boolean, List<Integer>>> supplier() {
        return () -> new HashMap<Boolean, List<Integer>>(){{
            put(Boolean.FALSE, new ArrayList<Integer>());
            put(Boolean.TRUE, new ArrayList<Integer>());
        }};
    }

    @Override
    public BiConsumer<Map<Boolean, List<Integer>>, Integer> accumulator() {
        return (acc, i) -> acc.get(isPrime3(acc.get(true), i)).add(i);
    }

    @Override
    public Function finisher() {
        return Function.identity();
    }

    @Override
    public BinaryOperator<Map<Boolean, List<Integer>>> combiner() {
        return (m1, m2) -> {
            m1.get(Boolean.FALSE).addAll(m2.get(Boolean.FALSE));
            m1.get(Boolean.TRUE).addAll(m2.get(Boolean.TRUE));
            return m1;
        };
    }

    @Override
    public Set<java.util.stream.Collector.Characteristics> characteristics() {
        return Collections.unmodifiableSet(EnumSet.of(java.util.stream.Collector.Characteristics.IDENTITY_FINISH));
    }

实现Collector接口




    public static Map<Boolean, List<Integer>> partitionPrime2(int n){
        return IntStream.rangeClosed(2, n).boxed()
                .collect(new PrimeNumbersCollector());
    }

    public static boolean isPrime3(List<Integer> primes, int n){
        int squareRoot = (int)Math.sqrt((double)n);
        return takeWhile(primes, (i) -> i>n?true:false).stream().noneMatch(i -> n%i==0);
    }

    public static List<Integer> takeWhile(List<Integer> list, Predicate<Integer> predicate){
        int i = 0;
        for(Integer item : list){
            if(predicate.test(item)){
                return list.subList(0, i);
            }
            i++;
        }
        return list;
    }

工具方法

    public static void main(String[] args) {
        System.out.println(partitionPrime2(100));
    }

测试用例

{false=[4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99, 100], true=[2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97]}