#! /usr/bin/perl -w
#
# Permutations (recursive)
# Monday June 22, 1998
#

sub
permute
{
  my @L = @{$_[0]};
  my $n = $#L;
  my (@pm, @result) = ((), ());
  if ($n == 0) {
    @result = ([$L[0]]);
  } else {
    my ($hd, @tail) = @L;
    my $ptail = permute(\@tail);
    foreach $e (@{$ptail}) {
      @pm = ();
      for ($i=0; $i<=$n; $i++) {
        @pm = @{$e};
        $pm[$n] = $pm[$i];
        $pm[$i] = $hd;
        @result = ([@pm], @result);
      }
    }
  }
  return \@result;
}

my $index = 1;
my $l = permute(\@ARGV);
$~ = 'STDOUT_TOP';
write;
foreach $e (@{$l}) {
  $permutation = "@{$e}";
  $~ = 'STDOUT';
  write;
  $index++;
}

format STDOUT_TOP =
      # Permutation
        -----------
.
format STDOUT =
@>>>>>> @<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
"[$index]", $permutation
.