Given a set of distinct integers, nums, return all possible subsets.Note: The solution set must not contain duplicate subsets.For example,If nums = [1,2,3], a solution is:[  [3],  [1],  [2],  [1,2,3],  [1,3],  [2,3],  [1,2],  []]

public class Solution {    public List<List<Integer>> subsets(int[] nums) {        if(nums==null){            return null;        }        List<List<Integer>> resList=new ArrayList<List<Integer>>();        List<Integer> item=new ArrayList<Integer>();        Arrays.sort(nums);        backTracking(nums, 0, item, resList);        resList.add(new ArrayList<Integer>());        return resList;    }        public void backTracking(int[] nums, int start, List<Integer> item,  List<List<Integer>> resList){                for(int i=start; i<nums.length; i++){            item.add(nums[i]);            resList.add(new ArrayList<Integer>(item));            backTracking(nums, i+1, item, resList);            item.remove(item.size()-1);        }    }}