Subsets II

public class Solution {
    public ArrayList<ArrayList<Integer>> subsetsWithDup(int[] num) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        ArrayList<Integer> list = new ArrayList();
        if(num == null)
            return result;
        Arrays.sort(num);
        generate(num, 0, result, list);
        return result;
    }
    
    private void generate(int[] num, int start, ArrayList<ArrayList<Integer>> result, ArrayList<Integer> list){
        ArrayList<Integer> tmp = new ArrayList<Integer>();
        tmp.addAll(list);
        result.add(tmp);
        
        for(int i = start; i < num.length; i++){
            if(i == start || (i > start && num[i] != num[i-1])){
                list.add(num[i]);
                generate(num, i+1, result, list);
                list.remove(list.size()-1);
            }
        }
    }
}