code: void markRow(int i, int marking) {
          for (int j = (i * mCols), end = j + mCols; j < end; j++)
              if (data[j] > 0) data[j] = marking;
      }
docs: Mark all values in row i allowing it to be reset later.
  
  @param i       row index
  @param marking the marking to store (should be negative)