Method helper

java/0078-subsets.java:13–29

(
        List<List<Integer>> ans,
        int start,
        int[] nums,
        List<Integer> list
    )

    }

    public void helper(
        List<List<Integer>> ans,
        int start,
        int[] nums,
        List<Integer> list
    ) {
        if (start >= nums.length) {
            ans.add(new ArrayList<>(list));
        } else {
            // add the element and start the  recursive call
            list.add(nums[start]);
            helper(ans, start + 1, nums, list);
            // remove the element and do the backtracking call.
            list.remove(list.size() - 1);
            helper(ans, start + 1, nums, list);
        }
    }
}