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.

COPYRIGHT AND LICENSE

    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.

