week 4 90. Subsets II

public class Solution {
    public List<List<Integer>> subsetsWithDup(int[] nums) {
        List<List<Integer>> res = new ArrayList<List<Integer>>();
        if (nums == null || nums.length == 0){
            res.add(new ArrayList<Integer>());
            return res;
        }
        Arrays.sort(nums);
        helper(res, new ArrayList<Integer>(), nums, 0);
        return res;
    }
    
    public void helper (List<List<Integer>> res, List<Integer> path, int [] nums, int pos){
        res.add (new ArrayList<Integer>(path));
        
        for(int i = pos; i < nums.length; i++){
            if(i != pos && nums[i] == nums[i-1]){
                continue;
            }
            path.add(nums[i]);
            helper(res, path, nums, i+1);
            path.remove(path.size() - 1);
        }
        return;
    }
}