while (<DATA>) {
   chomp;
   if ( /^(?:([smtwhfa])(?!.*\1))*$/ ) {
      print "$_ : OK\n";
   } else {
      print "$_ : Not OK\n";
   }
}

__DATA__
swma
smqa
smsa
fhtm
ttma
t2ms

__END__
swma : OK
smqa : Not OK
smsa : Not OK
fhtm : OK
ttma : Not OK
t2ms : Not OK