MakingProgramingGroup (better algorithm)

MakingProgramingGroup.java

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

public class MakingProgramingGroup {
    public static void main(String... args) {
        List<String> allMembers = Arrays.asList("1", "2", "3", "4", "5", "6");
        pairs(allMembers).forEach(group -> System.out.println("selectedGroup(better):" + group.stream().map(pair -> pair.stream().collect(Collectors.joining("&"))).collect(Collectors.joining(","))));
    }

    private static <T> List<List<List<T>>> pairs(List<T> list) {
        T first = list.get(0);
        List<T> rest = list.subList(1, list.size());
        return IntStream.range(0, rest.size())
                        .mapToObj(i -> Stream.concat(Stream.of(Arrays.asList(first, rest.get(i))),
                                                     IntStream.range(1, list.size() / 2)
                                                              .mapToObj(j -> pair(rest, i, j)))
                                             .collect(Collectors.toList()))
                        .collect(Collectors.toList());
    }

    private static <T> List<T> pair(List<T> list, int index, int offset) {
        return Arrays.asList(list.get((index - offset + list.size()) % list.size()),
                             list.get((index + offset) % list.size()));
    }
}

result

selectedGroup(better):1&2,6&3,5&4
selectedGroup(better):1&3,2&4,6&5
selectedGroup(better):1&4,3&5,2&6
selectedGroup(better):1&5,4&6,3&2
selectedGroup(better):1&6,5&2,4&3