week 4 78. Subsets

public class Solution {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        if (nums == null || nums.length == 0){
            res.add(new ArrayList<Integer>());
            return res;
        }
        helper(res, new ArrayList<Integer>(), nums, 0);
        return res;
    }
    public void helper(List<List<Integer>> res, List<Integer> path, int [] nums, int pos){
        res.add(new ArrayList<Integer>(path));
        
        for(int i = pos; i < nums.length; i++){
            path.add(nums[i]);
            helper(res, path, nums, i + 1);
            path.remove(path.size()-1);
        }
        return;
    }
}