public class Fermat {

    public static Set<List<String>> threadings(int n, Set<String> colours) {
        if (n == 0) {
            return Collections.singleton(new ArrayList<>());
        }

        Set<List<String>> previousThreadings = threadings(n - 1, colours);
        Set<List<String>> finalResult = new LinkedHashSet<>();
        for (List<String> beadList : previousThreadings) {
            for (String colour : colours) {
                List<String> newBeadList = new ArrayList<>(beadList);
                newBeadList.add(colour);
                finalResult.add(newBeadList);
            }
        }

        return finalResult;
    }

    public static void main(String[] args) {
        Set<String> colours = new HashSet<>();
        colours.add("red");
        colours.add("green");
        colours.add("blue");

        System.out.println(threadings(2, colours));
    }
}