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import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Random;
import java.util.Set;
import java.util.stream.IntStream;

public class CreateTeamSchedule {
    final static int numTeams = 10, numWeeks = 6;
    public static void main(String[] args) {
        List<Set<Integer>> usedMatchups = new ArrayList<>();
        for (int i = 1; i <= numWeeks; i++) {
            System.out.println("Week " + i + ": " + getMatchups(getRandomPermutation(), usedMatchups));
        }
    }

    public static List<Integer> getRandomPermutation() {
        List<Integer> perm = new ArrayList<Integer>(Arrays.asList(IntStream.rangeClosed(1, numTeams)
                                                    .boxed().toArray(Integer[]::new)));
        Collections.shuffle(perm , new Random());
        return perm;
    }

    public static List<Set<Integer>> getMatchups(List<Integer> list, List<Set<Integer>> usedMatchups) {
        List<Set<Integer>> matchups = new ArrayList<>();
        for (int i = 0; i < numTeams; i += 2) {
            matchups.add(new HashSet<>(list.subList(i, i + 2)));
        }
        if (Collections.disjoint(usedMatchups, matchups)) {
            usedMatchups.addAll(matchups);
        } else {
            matchups = getMatchups(getRandomPermutation(), usedMatchups);
        }
        return matchups;
    }
}

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$ javac CreateTeamSchedule.java

$ java CreateTeamSchedule
Week 1: [[7, 10], [2, 9], [4, 8], [1, 6], [3, 5]]
Week 2: [[2, 6], [5, 7], [1, 8], [9, 10], [3, 4]]
Week 3: [[3, 6], [8, 9], [4, 7], [5, 10], [1, 2]]
Week 4: [[1, 10], [2, 3], [6, 9], [7, 8], [4, 5]]
Week 5: [[3, 9], [1, 7], [2, 4], [6, 10], [5, 8]]
Week 6: [[8, 10], [2, 5], [4, 9], [6, 7], [1, 3]]

$ java CreateTeamSchedule
Week 1: [[1, 8], [2, 4], [3, 10], [6, 9], [5, 7]]
Week 2: [[4, 9], [1, 7], [8, 10], [2, 6], [3, 5]]
Week 3: [[2, 5], [1, 10], [6, 7], [3, 4], [8, 9]]
Week 4: [[1, 9], [5, 6], [2, 10], [3, 7], [4, 8]]
Week 5: [[1, 4], [2, 9], [7, 10], [5, 8], [3, 6]]
Week 6: [[4, 10], [5, 9], [3, 8], [2, 7], [1, 6]]

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