LeetCode:Subsets II

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],
  []
]

public class Solution {
    public ArrayList<ArrayList<Integer>> subsetsWithDup(int[] num) {
        
        if(num==null) return null;
        Arrays.sort(num);
        ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
        ArrayList<ArrayList<Integer>> prev = new ArrayList<ArrayList<Integer>>();   
            
        for(int i=num.length-1;i>=0;i--){
            if(i==num.length-1||num[i]!=num[i+1]||prev.size()==0){           
                prev = new ArrayList<ArrayList<Integer>>();
                for(int j=0;j<res.size();j++){
                        prev.add(new ArrayList<Integer>(res.get(j)));
                }
            }
            
            for(ArrayList<Integer> temp:prev){
                 temp.add(0,num[i]);
            }
                
            if(i==num.length-1||num[i]!=num[i+1]){
                ArrayList<Integer> temp1 = new ArrayList<Integer>();
                temp1.add(num[i]);
                prev.add(temp1);    
            }
            
            for(ArrayList<Integer> temp:prev){
                res.add(new ArrayList<Integer>(temp));
            }
        }
        res.add(new ArrayList<Integer>());
        return res;
    }
}