#!/usr/bin/perl -w
# DESCRIPTION: Generate permutations in lexicographic order
#       USAGE: ./permlex.pl <term1> <term2> <term3> .....

use strict;

die "bleah... nothing to permutate\n" if $#ARGV<0; 
my @terms = @ARGV; my $n = $#ARGV; my @a = (0..$n);
genperm(); exit(0);

sub genperm {
   print join(" ",@terms[@a]),"\n";
   my ($k,$j) = ($n-1,$n);
   $k-- while ($k>=0 and $a[$k]>$a[$k+1]);
   return(0) if ($k<0);
   $j--    while ($a[$k]>$a[$j]);
   swap($j,$k++); $j=$n;
   swap($j--,$k++) while ($j>$k);
   genperm();
}

sub swap {
   my ($i,$j) = @_; my $t = $a[$i];
   ($a[$i],$a[$j]) = ($a[$j],$t);
}
[download]

as you may see, it's a pure lexicographic permutations generator algorithm, as in the books ;-)

oh, not to forget, just checked up on cpan and found out there is a Algorithm::Permute module. here is a lame example for module users ;-)

#!/usr/bin/perl -w
use strict;
die "bleah... nothing to permutate\n" unless defined @ARGV; 
use Algorithm::Permute qw(permute permute_ref);
print join(" ", @$_), "\n" for permute(\@ARGV);
[download]

--
AltBlue.

your sub swap can be written without $t:

sub swap {
    my ($i,$j) = @_;
    @a[$i,$j] = @a[$j,$i];
}
[download]

lol, you bother to look upon this old piece of code :))

heh, of course that your snippet is good, but a swap routine could be written even simpler:

sub swap { reverse @_ }
[download]

... heh, it's not the case for that code thou, as the array is a global one :) cheers.

--
AltBlue.