How to generate the power-set of a given List?

Question

I\'m trying to generate a collection of all 2^N - 1 possible combinations of a given List of length N. The collection will map the number of elements in a combination to an

Answer 1

OP's solution moved from the question to an answer:

Thanks to previous answers, I came up with the following implementation:

public class OrderedPowerSet {
    private static final int ELEMENT_LIMIT = 12;
    private List inputList;
    public int N;
    private Map>> map = 
            new HashMap>>();

    public OrderedPowerSet(List list) {
        inputList = list;
        N = list.size();
        if (N > ELEMENT_LIMIT) {
            throw new RuntimeException(
                    "List with more then " + ELEMENT_LIMIT + " elements is too long...");
        }
    }

    public List> getPermutationsList(int elementCount) {
        if (elementCount < 1 || elementCount > N) {
            throw new IndexOutOfBoundsException(
                    "Can only generate permutations for a count between 1 to " + N);
        }
        if (map.containsKey(elementCount)) {
            return map.get(elementCount);
        }

        ArrayList> list = new ArrayList>();

        if (elementCount == N) {
            list.add(new LinkedHashSet(inputList));
        } else if (elementCount == 1) {
            for (int i = 0 ; i < N ; i++) {
                LinkedHashSet set = new LinkedHashSet();
                set.add(inputList.get(i));
                list.add(set);
            }
        } else {
            list = new ArrayList>();
            for (int i = 0 ; i <= N - elementCount ; i++) {
                @SuppressWarnings("unchecked")
                ArrayList subList = (ArrayList)((ArrayList)inputList).clone();
                for (int j = i ; j >= 0 ; j--) {
                    subList.remove(j);
                }
                OrderedPowerSet subPowerSet = 
                        new OrderedPowerSet(subList);

                List> pList = 
                        subPowerSet.getPermutationsList(elementCount-1);
                for (LinkedHashSet s : pList) {
                    LinkedHashSet set = new LinkedHashSet();
                    set.add(inputList.get(i));
                    set.addAll(s);
                    list.add(set);
                }               
            }
        }

        map.put(elementCount, list);

        return map.get(elementCount);
    }
}