On Mon, Mar 4, 2013 at 7:35 PM, Stefan Strasser <strasser@uni-bremen.de>wrote:
Am 04.03.2013 08:48, schrieb Martin Knoblauch Revuelta:
Do you mean that you would declare them RandomAccess iterators?
We can expect to have containers with millions of elements. For that size, O(log N) is about 20 times faster than O(log N log N). That makes a big difference.
isn't that a reason for providing optimized specializations of some STL algorithms, instead of introducing another iterator category?
how would a new iterator category even help? as long as your iterator is a forward iterator, the user is allowed to call std::binary_search on your iterator, which uses the same algorithm on any iterator category. (only functions used by binary_search like std::advance are specialized on the category) where in all this would your tree-optimized binary_search code be called?
the standard doesn't require random access iterator ops to be constant time.
Unfortunately, there is a problem of iterator categories with augmented trees. The C++ standard specifies computational complexity for iterator operations, although they are not shown in tables, since all of them are required to be constant time. In both C++03 and C++11 this is formulated in the section 24.1.8. IMO, the problem is rather theoretical than practical. First of all, in systems with virtual memory management the value of "constant time" can vary by almost two factors for array based and dynamically allocated data structures. This is the reason why in some cases dumb algorithms using std::vector outperform smart algorithms using trees. Second, STL specification ignores the main theoretical parameter of user algorithms - the total computational cost. This aspect has been discussed in the very first message of this thread. Third, augmented trees easily bypass these C++ restrictions, since they provide wider sets of efficient operations and can replace standard containers through existing interfaces. Also, I do not consider adding new category of iterators useful for the reason that it works against generality by increasing the number of types. The generalization or abstraction method reduces all the specific types to one "ideal type". The generalization also means more unified and coherent interfaces for various types that support the interface of this "ideal type". Regards, Vadim Stadnik