code: private Border getBorder(int row, int column)
      {
          if (row % 3 == 2)
          {
              switch (column % 3)
              {
                  case 2: return BOTTOM_RIGHT_BORDER;
                  case 0: return BOTTOM_LEFT_BORDER;
                  default: return BOTTOM_BORDER;
              }
          }
          else if (row % 3 == 0)
          {
              switch (column % 3)
              {
                  case 2: return TOP_RIGHT_BORDER;
                  case 0: return TOP_LEFT_BORDER;
                  default: return TOP_BORDER;
              }
          }
  
          switch (column % 3)
          {
              case 2: return RIGHT_BORDER;
              case 0: return LEFT_BORDER;
              default: return null;
          }
      }
docs: Get appropriate border for cell based on its position in the grid.