>>442 Perl5、"6"も文字列に含めれば、4

for (<DATA>) {
 @a = /(\w)/g;
 %h = map{$_ => 1} @a;
 $s = $a[0].join('', sort keys %h).$a[-1];
 print "$_ -> $s\n";
 $g{$s}++;
}
print keys(%g)."\n";
__DATA__
6
programming
odai
prorgamnimg
oadi
pgorgamming
idao

実行結果
~ $ perl 17_442_similstr.pl
666 <- 6
pagimnoprg <- programming
oadioi <- odai
pagimnoprg <- prorgamnimg
oadioi <- oadi
pagimnoprg <- pgorgamming
iadioo <- idao
4