答案

public class Solution {
    public void quickSort(int []S,int startIndex,int endIndex){
        if(startIndex>=endIndex){
            return;
        }
        int middleIndex=(startIndex+endIndex)/2;
        int p=S[middleIndex];
        S[middleIndex]=S[startIndex];
        S[startIndex]=p;
        int i=startIndex+1;
        int j=endIndex;
        for(;i<j;){
            while(i<j)
            {
                if(S[i]>=S[startIndex])
                {
                    break;
                }
                i++;
            }
            while(i<j)
            {
                if(S[j]<S[startIndex])
                {
                    break;
                }
                j--;
            }
            p=S[i];
            S[i]=S[j];
            S[j]=p;
        }
        if(S[i]>S[startIndex])
        {
            i--;
        }
        p=S[i];
        S[i]=S[startIndex];
        S[startIndex]=p;
        quickSort(S,startIndex,i-1);
        quickSort(S,i+1,endIndex);
        
    }
    public List<List<Integer>> subsets(int[] S) {
        List<List<Integer>> result=new LinkedList<List<Integer>>();
        List<List<Integer>> tmp=new LinkedList<List<Integer>>();
        List<Integer> p=new LinkedList<Integer>();
        result.add(p);
        if(S==null||S.length<=0)
        {
            return result;
        }
        int LEN=S.length;
        quickSort(S,0,LEN-1);
        for(int i=0;i<LEN;i++){
            tmp.clear();
            for(List<Integer>list:result){
                p=new LinkedList<Integer>();
                p.addAll(list);
                p.add(S[i]);
                tmp.add(p);
            }
            result.addAll(tmp);
        }
        return result;
    }
}