use strict;
use warnings;

my $good = [qw( allo mallo malo)];
my $bad  = [qw( tillo sillo sallo)];

foreach my $list ($good,$bad){
    my $has_unique;
    foreach my $word(@$list){
          my %chars;
          $chars{$_}++ for ($word =~ /./g);
          if (scalar keys %chars == length $word){
              # print "$word has no repeated letters";
              $has_unique++;
          }
    }
    print +(join ' ', @$list),"\n" if $has_unique;
}

# output

allo mallo malo