interesting approach that reminded me about some old project that needed some permutations generations stuff... so, i've checked up that code and here i come with a reviewed standalone version:
#!/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.

In reply to RE: Permutations and combinations by AltBlue
in thread Permutations and combinations by merlyn

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