I've been scouring CPAN directly and via Google for a module that will iterate permutations in reverse order, but have come up empty. I would rather not roll my own.

I ask because I'm working on a search algorithm where I need to find the maximum permutation that meets the search criteria, but with ~8.7e10 permutations, searching them all is a huge waste.

I want to be able to do something like the below code. Of course Algorithm::Permute has no prev() method (nor does it actually guarantee any order), and neither do any of the other permutation/combinatorics modules I could find.

Alternatively, is there a clever way to (ab)use ascending permutations to get descending ones that I can't see right now?

use Algorithm::Permute;

say join ",",search(reverse (1..14));

sub search {
    my $p = new Algorithm::Permute(\@_);
    while (my @a = $p->prev) {
        return @a if copasetic(@a);
    }
}

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In reply to Permutations in reverse order by wanna_code_perl

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