Subsets

Given a set of distinct integers, 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 = [1,2,3], a solution is:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

public class Solution {
    public ArrayList<ArrayList<Integer>> subsets(int[] S) {
		// Start typing your Java solution below
		// DO NOT write main() function
		ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
		ArrayList<Integer> set = new ArrayList<Integer>();
		Arrays.sort(S);
		subsets(res, set, S, 0);
		return res;
	}
	public void subsets(ArrayList<ArrayList<Integer>> res, ArrayList<Integer> sets, int[] S, int index){
		if(index == S.length){
			res.add(new ArrayList<Integer>(sets));
		}
		else{
			sets.add(S[index]);
			subsets(res, sets, S, index + 1);// contains current index element
			sets.remove(sets.size() - 1);
			subsets(res, sets, S, index + 1);// do not contain current index element
		}
	}
}

Remember to sort array S as a requirement from the question. Not a necessary process.