c:\@Work\Perl\monks>perl -wMstrict -le
"my $x = 'TTT0TTTTT';
 my $y = 'TTTTTTTT';
 my $z = 'TBTTTTT';
 ;;
 print qq{only one of '$_'} for one_only($x, $y, $z);
 ;;
 sub one_only {
   my %freq;
   return
     grep $freq{$_} == 1,
     map  ++$freq{$_} && $_,
     map  split('', $_),
     @_
     ;
   }
"
only one of '0'
only one of 'B'