/** A {@code RegularImmutableTable} optimized for sparse data. */
@GwtCompatible
@Immutable(containerOf = {"R", "C", "V"})
final class SparseImmutableTable<R, C, V> extends RegularImmutableTable<R, C, V> {
  static final ImmutableTable<Object, Object, Object> EMPTY =
      new SparseImmutableTable<>(
          ImmutableList.<Cell<Object, Object, Object>>of(), ImmutableSet.of(), ImmutableSet.of());

  private static final ImmutableSet<Integer> COLUMN_SPACE = ImmutableSet.of(1, 2);

  private static final SparseImmutableTable<Character, Integer, String> SPARSE =
      new SparseImmutableTable<>(CELLS.asList(), ROW_SPACE, COLUMN_SPACE);

  private static final DenseImmutableTable<Character, Integer, String> DENSE =

    return (cellList.size() > (((long) rowSpace.size() * columnSpace.size()) / 2))
        ? new DenseImmutableTable<R, C, V>(cellList, rowSpace, columnSpace)
        : new SparseImmutableTable<R, C, V>(cellList, rowSpace, columnSpace);
  }

  /**
   * @throws IllegalArgumentException if {@code existingValue} is not null.
   */
  /*