sub permute{
  my ($prefix,$c,@arrays)=@_;
  my @ret=();
  foreach(@$c){
    my $f=$prefix.$_;
    if(scalar(@arrays)==0){
      push @ret,$f;
    }else{
      push @ret,@{permute($f,@arrays)};
    }
  }
  return \@ret;
}

my $perms=permute('',['C','A','T'],['D','O','G'],['B','I','R',D']);