oracular (3) Algorithm::Permute.3pm.gz

Provided by: libalgorithm-permute-perl_0.17-1build3_amd64 bug

NAME
       Algorithm::Permute - Handy and fast permutation with object oriented interface


SYNOPSIS
         use Algorithm::Permute;

         # default is to create n of n objects permutation generator
         my $p = Algorithm::Permute->new(['a'..'d']);

         # but also you can create r of n objects permutation generator, where r <= n
         my $p = Algorithm::Permute->new([1..4], 3);

         while (my @res = $p->next) {
           print join(", ", @res), "\n";
         }

         # and this one is the speed demon:
         my @array = (1..9);
         Algorithm::Permute::permute { print "@array\n" } @array;


DESCRIPTION
       This handy module makes performing permutation in Perl easy and fast, although perhaps its algorithm is
       not the fastest on the earth.  It supports permutation r of n objects where 0 < r <= n.


METHODS
       new [@list]
           Returns a permutor object for the given items.

       next
           Returns a list of the items in the next permutation.  The order of the resulting permutation is the
           same as of the previous version of "Algorithm::Permute".

       peek
           Returns the list of items which will be returned by next(), but doesn't advance the sequence. Could
           be useful if you wished to skip over just a few unwanted permutations.

       reset
           Resets the iterator to the start. May be used at any time, whether the entire set has been produced
           or not. Has no useful return value.


CALLBACK STYLE INTERFACE
       Starting with version 0.03, there is a function - not exported by default - which supports a callback
       style interface:

       permute BLOCK ARRAY
           A block of code is passed, which will be executed for each permutation. The array will be changed in
           place, and then changed back again before "permute" returns. During the execution of the callback,
           the array is read-only and you'll get an error if you try to change its length. (You can change its
           elements, but the consequences are liable to confuse you and may change in future versions.)

           You have to pass an array, it can't just be a list. It does work with special arrays and tied arrays,
           though unless you're doing something particularly abstruse you'd be better off copying the elements
           into a normal array first. Example:

            my @array = (1..9);
            permute { print "@array\n" } @array;

           The code is run inside a pseudo block, rather than as a normal subroutine. That means you can't use
           "return", and you can't jump out of it using "goto" and so on. Also, "caller" won't tell you anything
           helpful from inside the callback. Such is the price of speed.

           The order in which the permutations are generated is not guaranteed, so don't rely on it.

           The low-level hack behind this function makes it currently the fastest way of doing permutation among
           others.


COMPARISON
       I've collected some Perl routines and modules which implement permutation, and do some simple benchmark.
       The whole result is the following.

       Permutation of eight scalars:

         Abigail's                     :  9 wallclock secs ( 8.07 usr +  0.30 sys =  8.37 CPU)
         Algorithm::Permute            :  5 wallclock secs ( 5.72 usr +  0.00 sys =  5.72 CPU)
         Algorithm::Permute qw(permute):  2 wallclock secs ( 1.65 usr +  0.00 sys =  1.65 CPU)
         List::Permutor                : 27 wallclock secs (26.73 usr +  0.01 sys = 26.74 CPU)
         Memoization                   : 32 wallclock secs (32.55 usr +  0.02 sys = 32.57 CPU)
         perlfaq4                      : 36 wallclock secs (35.27 usr +  0.02 sys = 35.29 CPU)

       Permutation of nine scalars (the Abigail's routine is commented out, because it stores all of the result
       in memory, swallows all of my machine's memory):

         Algorithm::Permute            :  43 wallclock secs ( 42.93 usr +  0.04 sys = 42.97 CPU)
         Algorithm::Permute qw(permute):  15 wallclock secs ( 14.82 usr +  0.00 sys = 14.82 CPU)
         List::Permutor                : 227 wallclock secs (226.46 usr +  0.22 sys = 226.68 CPU)
         Memoization                   : 307 wallclock secs (306.69 usr +  0.43 sys = 307.12 CPU)
         perlfaq4                      : 272 wallclock secs (271.93 usr +  0.33 sys = 272.26 CPU)

       The benchmark script is included in the bench directory. I understand that speed is not everything. So
       here is the list of URLs of the alternatives, in case you hate this module.

       •   Memoization is discussed in chapter 4 Perl Cookbook, so you can get it from O'Reilly:
           ftp://ftp.oreilly.com/published/oreilly/perl/cookbook

       •   Abigail's: http://www.foad.org/~abigail/Perl

       •   List::Permutor: http://www.cpan.org/modules/by-module/List

       •   The classic way, usually used by Lisp hackers: perldoc perlfaq4


ACKNOWLEDGEMENT
       In Edwin's words: Yustina Sri Suharini - my ex-fiance-now-wife, for providing the permutation problem to
       me.


SEE ALSO
       • Data Structures, Algorithms, and Program Style Using C - Korsh and Garrett

       • Algorithms from P to NP, Vol. I - Moret and Shapiro


AUTHOR
       Edwin Pratomo <edpratomo@cpan.org> was the original author.

       Stephan Loyd <sloyd@cpan.org> is co-maintainer after version 0.12.

       The object oriented interface is taken from Tom Phoenix's "List::Permutor".  Robin Houston
       <robin@kitsite.com> invented and contributed the callback style interface.


       This software is copyright (c) 1999 by Edwin Pratomo.

       This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5
       programming language system itself.