Classical combination problem.

1 class Solution { 2 public: 3     void getComb(vector
     
      
        > &result, vector
       
         &num, vector
        
          current, int index, int len) { 4         if (current.size() == len) { 5             result.push_back(current); 6             return; 7         } 8         for (int i = index; i < num.size(); i++) { 9             current.push_back(num[i]);10             getComb(result, num, current, i+1, len);11             current.pop_back();12         }13     }14     vector
         
          
            > subsets(vector
           
             &S) {15 vector
            
             
               > result;16 sort(S.begin(), S.end());17 for (int i = 0; i <= S.size(); i++) {18 getComb(result, S, vector
              
               (), 0, i);19 }20 return result;21 }22 };