/// <summary>
/// Creates an ordered array of subsetCount long indices that
/// constitute a subset of all longs in the range [0, count-1].
/// O(subsetCount * log(subsetCount)) for subsetCount << count.
/// NOTE: It is assumed that subsetCount is significantly smaller
/// than count. If this is not the case, use
/// CreateRandomSubsetOfSize instead.
/// WARNING: As subsetCount approaches count execution time
/// increases significantly.
/// </summary>
public static long[] CreateSmallRandomOrderedSubsetIndexArrayLong(
this IRandomUniform rnd, long subsetCount, long count)
{
var subsetIndexArray = rnd.CreateSmallRandomSubsetIndexArrayLong(subsetCount, count);
subsetIndexArray.QuickSortAscending();
return(subsetIndexArray);
}