[boost] [STL/Algorithm]Addin Combination against std::permutation?

From: Ð۽ܳ (benbearchen_at_[hidden])
Date: 2006-08-05 10:29:22

Hi!

   I wrote a Combination which is against to std::permutation.
It can enumerate all result of a combination, such as selecting 3
chars from "ABCDE", by `dictionary order'.  It's just like the
std::permutation.

   The code is published at
http://www.bxmy.org/code/combination.cpp.  And I wrote a article
about this Combination Algorithm in Chinese,
http://www.bxmy.org/article/combination.pdf.  Also, the code can
be found in the enclosure.

   The combination has at least three functions:
combination_adjust:  should be called for initialize the sequence;
next_combination:    get next combination, like next_permutation;
prev_combination:    get previous combination, like prev_permutation.

  This algorithm separates all elements into two parts. One is [first,
middle), the elements selected in. Other is [middle, last), the
elements selected out.  The steps are:

1) find the first element `Pout' in [first, middle) which should be
selected out.

2) find the first element `Qin' in [middle, last) which should be
selected in.

3) iter_swap(Pout, Qin).

4) merge [Pout+1, middle) and [Qin+1, last).

   It's simple and compatible with std::permutation well.  I hope that
it can be add into the STL.  They are couple.

Thanks.

Ben T. Bear