MakePairProgramingGroup.java

MakePairProgramingGroup.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.stream.Collectors;

public class MakePairProgramingGroup {

    public static void main(String... args) {
        List<String> allMembers = Arrays.asList("1", "2", "3", "4", "5", "6");
        List<List<String>> allPairs = makePairs(allMembers);
        allPairs.stream().forEach(pair -> System.out.println("pair:" + pair.stream().collect(Collectors.joining("&"))));

        List<List<List<String>>> allGroups = new ArrayList<>();
        makeGroup(allPairs, new ArrayList<>(), allGroups, allMembers.size() / 2);

        List<List<List<String>>> selectedGroups = selectGroup(allGroups);
        selectedGroups.stream().forEach(
                group -> System.out.println("selectedGroup:" + group.stream().map(pair -> pair.stream().collect(Collectors.joining("&"))).collect(Collectors.joining(","))));

    }

    static private <T> List<List<T>> makePairs(List<T> memberNames) {
        List<List<T>> allPairs = new ArrayList<>();
        for (int i = 0; i < memberNames.size() - 1; i++) {
            for (int j = i + 1; j < memberNames.size(); j++) {
                List<T> pair = new ArrayList<>();
                pair.add(memberNames.get(i));
                pair.add(memberNames.get(j));
                allPairs.add(pair);
            }
        }
        return allPairs;
    }

    static private <T> void makeGroup(List<List<T>> pairs, List<List<T>> currentGroup, List<List<List<T>>> groups, int maxGroupSize) {
        if (currentGroup.size() + 1 == maxGroupSize) {
            pairs.forEach(pair -> {
                List<List<T>> group = new ArrayList<>(currentGroup);
                group.add(pair);
                List<T> groupMembers = group.stream().flatMap(Collection::stream).collect(Collectors.toList());
                Set<T> distinctMembers = new HashSet<>(groupMembers);
                if (groupMembers.size() == distinctMembers.size()) {
                    groups.add(group);
                }
            });
        } else {
            for (int i = 0; i < pairs.size() - (maxGroupSize - currentGroup.size()); i++) {
                List<List<T>> group = new ArrayList<>(currentGroup);
                group.add(pairs.get(i));
                makeGroup(pairs.subList(1, pairs.size()), group, groups, maxGroupSize);
            }
        }
    }

    static private <T> List<List<List<T>>> selectGroup(List<List<List<T>>> groups) {
        List<List<List<T>>> selectedGroups = new ArrayList<>();
        groups.forEach(group -> {
            if (selectedGroups.stream().flatMap(g -> g.stream()).allMatch(pair -> !group.contains(pair))) {
                selectedGroups.add(group);
            }
        });
        return selectedGroups;
    }
}

result

pair:1&2
pair:1&3
pair:1&4
pair:1&5
pair:1&6
pair:2&3
pair:2&4
pair:2&5
pair:2&6
pair:3&4
pair:3&5
pair:3&6
pair:4&5
pair:4&6
pair:5&6
selectedGroup:1&2,3&4,5&6
selectedGroup:1&3,2&5,4&6
selectedGroup:1&4,2&6,3&5
selectedGroup:1&5,2&4,3&6
selectedGroup:1&6,2&3,4&5