Lintcode--Subsets

Despriction

Given a set of distinct integers, S, return all possible subsets.
Note:
Elements in a subset must be in non-descending order.
The solution set must not contain duplicate subsets.

For example
If S = [1,2,3], a solution is:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

code

class Solution {
        /**
         * @param S: A set of numbers.
         * @return: A list of lists. All valid subsets.
         */
        public ArrayList<ArrayList<Integer>> subsets(int[] nums) {
            // write your code here
            ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
            if (nums == null || nums.length == 0) {
                return result;
            }
            Arrays.sort(nums);
            ArrayList<Integer> list = new ArrayList<Integer>();
            subsetsHelp(result, list, nums, 0);
            return result;
        }

        private void subsetsHelp(ArrayList<ArrayList<Integer>> result, ArrayList<Integer> list, int[] nums, int pos) {
            result.add(new ArrayList<Integer>(list));
            for (int i = pos; i < nums.length; i++) {
                list.add(nums[i]);
                subsetsHelp(result, list, nums, i + 1);
                list.remove(list.size() - 1);
            }
        }
}