78.Subsets

class Solution {
    public List<List<Integer>> subsets(int[] nums) {
        List<List<Integer>> ans = new ArrayList<>();
        helper(ans, new ArrayList<>(), nums, 0);
        return ans;
    }

    public void helper(List<List<Integer>> ans, List<Integer> comb, int[] nums, int start){
        ans.add(new ArrayList<>(comb));
        for(int i = start; i < nums.length; i++){
            comb.add(nums[i]);
            helper(ans, comb, nums, i + 1);
            comb.remove(comb.size() - 1);
        }
        return;
    }
}