public List<List<Integer>> subsets(int[] nums) {

List<List<Integer>> results = new ArrayList<>();

if(nums==null||nums.length==0) return results;

ArrayList<Integer> subset = new ArrayList<>();

dfsHelper(0,nums,subset,results);

return results;

}

private void dfsHelper(int start, int[] nums, ArrayList<Integer> subset, List<List<Integer>> results){

results.add(new ArrayList(subset));

for(int i = start; i<nums.length; i++){

subset.add(nums[i]);

dfsHelper(i+1,nums,subset,results);

subset.remove(subset.size()-1);

}

}

}