public static T QuickSelect <T>(this IEnumerable <T> source, int begin, int end, int index, SelectType type, Func <T, T, bool> comparer)
{
List <T> list = source.ToList();
return(QuickSelectList(list, begin, end, index, type, comparer));
}
private static T QuickSelectList <T>(List <T> source, int begin, int end, int index, SelectType type, Func <T, T, bool> comparer)
{
if (end - begin + 1 >= index)
{
int partition = 0;
if (type == SelectType.HEADER)
{
partition = CommonSort.Partition(source, begin, end, begin, comparer);
}
else if (type == SelectType.END)
{
partition = CommonSort.Partition(source, begin, end, end, comparer);
}
else
{
partition = CommonSort.Partition(source, begin, end, (begin + end) / 2, comparer);
}
if (index + begin < partition)
{
QuickSelectList(source, begin, partition, index, type, comparer);
}
else if (index + begin > partition)
{
QuickSelectList(source, partition + 1, end, index - partition + begin - 1, type, comparer);
}
else
{
return(source[partition]);
}
}
throw new IndexOutOfRangeException();
}
