On Jan 4, 2011, at 11:05 AM, Anthony Williams wrote:
Howard Hinnant <howard.hinnant@gmail.com> writes:
On Jan 4, 2011, at 6:22 AM, Christopher Jefferson wrote:
On 4 Jan 2011, at 03:40, Howard Hinnant wrote:
Warming this up for tr2:
http://home.roadrunner.com/~hinnant/combinations.html
Comments welcome. Real world use welcome.
For TR2, it would be nice to produce a range object, so we could write:
for(perm: reversible_permutation(first, mid, last) ) f(perm);
Not positive, but I believe (if one could figure out how to code it) would suffer the exponential cost of incrementation demonstrated for next_partial_permutation and next_combination in "Performance Considerations" shown in:
Couldn't the range adaptor object --- or the iterators generated from it --- store the intermediate information about where in the series of swaps it was? Sort of a continuation in your for_each_permutation() functions.
I don't know. Show me the code. :-) Hervé Brönnimann wrote a high quality implementation of next_combination which stored this information in the sorted-but-permuted sequence (just like std::next_permutation): http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2639.pdf And such an algorithm could be the operator++() for a range adaptor. But my tests are showing this approach to be very expensive for some cases (see the plots in my paper). -Howard