Subsets with repeated elements

Given a collection of integers that might contain duplicates, S, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• The solution set must not contain duplicate subsets.

For example,
If S = [1,2,2], a solution is:

[  [2],  [1],  [1,2,2],  [2,2],  [1,2],  []]
    public ArrayList<ArrayList<Integer>> subsetsWithDup(int[] num) {        // Note: The Solution object is instantiated only once and is reused by each test case.        Arrays.sort(num);        return help(num, 0);    }        public ArrayList<ArrayList<Integer>> help(int[] num, int index) {        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();        Set<ArrayList<Integer>> set = new HashSet<ArrayList<Integer>>();        if(index == num.length) {            result.add(new ArrayList<Integer>());            return result;        }        for(ArrayList<Integer> sub : help(num, index + 1)) {            set.add(sub);            ArrayList<Integer> a = new ArrayList<Integer>();            a.add(num[index]);            a.addAll(sub);            if(!set.contains(a)) set.add(a);        }        result.addAll(set);        return result;    }