[Leetcode] Subsets II

Given a collection of integers that might contain duplicates, 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 = [1,2,2], a solution is:

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

Solution:

 public class Solution {
     public List<List<Integer>> subsetsWithDup(int[] num) {
         Arrays.sort(num);
         List<List<Integer>> result = new ArrayList<List<Integer>>();
         List<Integer> al = new ArrayList<Integer>();
         dfs(result, al, num, 0);
         return result;
     }

     private void dfs(List<List<Integer>> result, List<Integer> al, int[] s,
             int start) {
         // TODO Auto-generated method stub
         result.add(new ArrayList<Integer>(al));
         for (int i = start; i < s.length; ++i) {
             al.add(s[i]);
             dfs(result, al, s, i+1);
             al.remove(al.size()-1);
             while((i+1<s.length)&&(s[i]==s[i+1]))
                 ++i;
         }
     }
 }