=head1 Name
Math::Permute::List - Generate all permutations of a list.
=head1 Synopsis
use Math::Permute::List;
permute {say "@_"} qw(a b c);
# a b c
# a c b
# b a c
# c a b
# b c a
# c b a
=cut
use strict;
package Math::Permute::List;
sub permute(&@) # Generate all permutations of a list
{my $s = shift; # Subroutine to call to process each permutation
my $n = scalar(@_); # Size of array to be permuted
# return 0 unless $n; # Empty lists cannot be permuted - removed per Philipp Rumpf
my $l = 0; # Item being permuted
my @p = (); # Current permutations
my @P = @_; # Array to permute
my @Q = (); # Permuted array
my $p; $p = sub # Generate each permutation
{if ($l < $n)
{for(0..$n-1)
{if (!$p[$_])
{$Q[$_] = $P[$l];
$p[$_] = ++$l;
&$p();
--$l;
$p[$_] = 0;
}
}
}
else
{&$s(@Q);
}
};
&$p;
$p = undef; # Break memory loop per Philipp Rumpf
my $i = 1; $i *= $_ for 2..$n;
$i # Number of permutations
}
# Export details
require 5;
require Exporter;
use vars qw(@ISA @EXPORT $VERSION);
@ISA = qw(Exporter);
@EXPORT = qw(permute);
$VERSION = '1.007';
=head1 Description
Generate and process all the permutations of a list using the standard
Perl metaphor.
C returns the number of permutations in both scalar and array
context.
C is easy to use and fast. It is written in 100% Pure Perl.
Please note that the order in which the permutations are generated is
not guaranteed, so please do not rely on it.
=head1 Export
The C function is exported.
=head1 Installation
Standard Module::Build process for building and installing modules:
perl Build.PL
./Build
./Build test
./Build install
Or, if you're on a platform (like DOS or Windows) that doesn't require
the "./" notation, you can do this:
perl Build.PL
Build
Build test
Build install
=head1 Author
PhilipRBrenan@appaapps.com
http://www.appaapps.com
=head1 Acknowledgements
With considerable, cogent and unfailing help from Philipp Rumpf for which I am indebted.
http://www.appaapps.com
=head1 See Also
=over
=item L
=item L
=item L
=item L
=item L
=back
=head1 Copyright
Copyright (c) 2009 Philip R Brenan.
This module is free software. It may be used, redistributed and/or
modified under the same terms as Perl itself.
=cut