Main.java

import java.util.ArrayList;
import java.util.BitSet;
import java.util.List;
import java.util.stream.IntStream;
import java.util.stream.LongStream;

import static java.util.stream.Collectors.toList;

public class Main {
    public static List<Long> binaryNialpdromes(int n) {
        final var ret = new ArrayList<Long>(n * (n + 1) / 2);

        for (int i = 0; i <= n; i++) {
            for (int j = 0; j < i; j++) {
                ret.add((long) (Math.pow(2.0, i) - Math.pow(2.0, j)));
            }
        }

        return ret;
    }

    public static List<List<Integer>> contiguousSubsequences(List<Integer> list) {
        return binaryNialpdromes(list.size())
                .stream()
                .map(n -> BitSet.valueOf(new long[]{n}))
                .map(BitSet::stream)
                .map(s -> s.boxed().map(list::get).collect(toList()))
                .collect(toList());
    }

    public static List<List<Integer>> powerSet(List<Integer> list) {
        return LongStream
                .range(0, (int) Math.pow(2.0, list.size()))
                .boxed()
                .map(n -> BitSet.valueOf(new long[]{n}))
                .map(BitSet::stream)
                .map(s -> s.boxed().map(list::get).collect(toList()))
                .collect(toList());
    }

    public static void main(String[] args) {
        System.out.println("Hello world!");
        final var list = IntStream.range(0, 7).boxed().collect(toList());

        System.out.println("Length of power set of " + list + ":");
        System.out.println(powerSet(list));
        System.out.println("Length of set of all subsequences of " + list + ":");
        System.out.println(contiguousSubsequences(list));
    }
}