90. Subsets II

Given a collection of integers that might contain duplicates, nums, return all possible subsets.

Note: The solution set must not contain duplicate subsets.

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

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

public class Solution {
    public List<List<Integer>> subsetsWithDup(int[] num) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        if(num == null || num.length == 0) {
            return result;
        }
        ArrayList<Integer> list = new ArrayList<Integer>();
        Arrays.sort(num);  
        subsetsHelper(result, list, num, 0);

        return result;        
    }
    
    private void subsetsHelper(List<List<Integer>> result, ArrayList<Integer> list, int[] num, int pos) {
        result.add(new ArrayList<Integer>(list));
        for (int i = pos; i < num.length; i++) {
            if(i != pos && num[i] == num[i - 1]){
                continue;
            }
            list.add(num[i]);
            subsetsHelper(result, list, num, i + 1);
            list.remove(list.size() - 1);
        }
    }

}