code: public int[] getRoles() {
          List<Integer> roles = new ArrayList<Integer>();
          for(int i = 0; i < data.length; i++) {
              if(data[i] != null) {
                  roles.add(i);
              }
          }
          
          int[] res = new int[roles.size()];
          for(int i = 0; i < res.length; i++) {
              res[i] = roles.get(i);
          }
          return res;
      }
docs: Returns the roles stored in this data structure.
  @return