// Determines the dValue given set
// For a set x, d is defined as follows:
// d(N) = 0
// d(x) = 1 + min(max v in x, max v not in x)
private static int DetermineDValue(BitSet set)
{
BitSet _set = !set;
if (set.IsEmpty || _set.IsEmpty)
return 0;
return 1 + Math.Min(set.Last(), _set.Last());
}