$string='GAAGANNNNNNNNNNACGCATACTACCGGTGCCCAGCTGCCATNNNNNNNGAGAGAGATCNNNNNNGAGANNNNNNNATTCTCTNNNNCTCAGATCCNNNNNNNNNNNNNNNNNNNNNGAGA'; 
(@ns) = $string =~ /N+/g; 
print 'Länge der Ns',"\n";
for (sort @ns) {
   print length($_),"\n";
}