[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;
        }
    }
}