my %sec;
my $newsecret;
for my $char (split //, $secret){
  next if exists $sec{$char};
  $newsecret .= $char;
  $sec{$char}++;
}

##</code><code>##

$newsecret = join '', map { ??? } split //, $secret;

##</code><code>##

my $newsecret = join '', map { my $char=$_; $_='' if exists $sec{$_}; $sec{$char}++} split //, $secret;

##</code><code>##

-----------------------------------
--the good, the bad and the physi--
-----------------------------------