sub matchss {
  my($ss, $str) = @_;
  my @state = (1, (0) x length($ss));
  my %index;
  unshift @{ $index{substr $ss, $_ - 1, 1} }, $_ for 1 .. length($ss);
  for (split //, $str) { 
    $state[$_] += $state[$_ - 1] for @{ $index{$_} || [] };
  } 
  pop @state;
}