class Solution {

    public List<List<Integer>> answer = new ArrayList();

    public int[] nums_util;

    public List<List<Integer>> subsets(int[] nums) {
        nums_util = nums;
        List<Integer> utilList = new ArrayList();
        for(int i = 0;i<=nums.length;i++){
            helper(i,0,utilList);
        }
        return answer;
    }

    public void helper(int goalLength,int startIndex,List<Integer> currentBuiltList){
        if(currentBuiltList.size() == goalLength){
            answer.add(new ArrayList(currentBuiltList));
            return;
        }
        for(int i = startIndex;i<nums_util.length;i++){
            currentBuiltList.add(nums_util[i]);
            helper(goalLength,i+1,currentBuiltList);
            currentBuiltList.remove(currentBuiltList.size() - 1);
        }
    }
}