返回集合的所有子集

typedef vector<int> vi;
typedef vector<vector<int>> vvi;
vvi get_subsets1(int a[],int idx,int n)
{
    vvi subsets;
    if(idx==n)
    {   //返回空集
        vi subset;
        subsets.push_back(subset);
    }
    else
    {   
        vvi rsubsets=get_subsets1(a,idx+1,n);//返回某个集合
        //将该元素与返回集合的各元素合并，得到各个集合
        int v=a[idx];
        for(int i=0;i<rsubsets.size();i++)
        {
            vi subset=rsubsets[i];
            subsets.push_back(subset);
            subset.push_back(v);
            subsets.push_back(subset);
        }
    }
    return subsets;
}
void print_subsets(vvi sub)
{
    for(int i=0;i<sub.size();i++)
    {
        vi subset=sub[i];
        for(int j=0;j<subset.size();j++)
        {
            cout<<subset[j]<<"";
        }
        cout<<endl;
    }
}
int main(){
    int a[] = {
        1, 2, 3, 4
    };
    vvi sub1 = get_subsets1(a, 0, 4);
    print_subsets(sub1);
    system("pause");
    return 0;
}