[boost] Re: [boost] [gacap]Is any interesting to "Generating All Combinations and Permutations"£¿

From: Ben Bear (benbearchen_at_[hidden])
Date: 2007-11-12 20:27:01

2007/11/13, Hervé Brönnimann <hervebronnimann_at_[hidden]>:
> Ben, Giovanni:  I've been giving some thought to this and I don't
> think that I'd want to propose next_permutation(first, middle, last)
> to the standard.   It is easily achievable through next_combination
> (first, middle, last) then going over all the permutations via
> next_permutation(first, middle), in a loop.  Granted, the order of
> the permutations is a bit different that way, but frankly nobody
> should care, the order is well specified (just not the lexicographic
> order on the permutations, but the lexicographic order on the
> underlying combination and if this combination is the same, the
> lexicographic order of the permutations), and it makes the would-be
> proposal a pure library extension -- so much easier to pass by the
> committee.
>

Then, what about next_permutation(first, middle, last, comp)?  Don't
propose it too?

next_permutation(first, middle, last) is easy to be implemented:

bool next_permutation(first, middle, last)
{
  // actually, sort only need once, that's what init()/adjust() does
  sort (middle, last);
  reverse (middle, last);
  return next_permutation(first, last);
}

If only propose combination's functions, there's eight functions:

init_combination(first, middle, last, min);
init_combination(first, middle, last, min, comp);
adjust_combination(first, middle, last);
adjust_combination(first, middle, last, comp);

next_combination(first, middle, last);
next_combination(first, middle, last, comp);
prev_combination(first, middle, last);
prev_combiantion(first, middle, last, comp);

I think that, whether the init() and adjust() can be removed, but
leave the initialization to the  callers, then only four functions is
needed.  I think this is not a good idea.