# 123 chars
sub g {
  #23456789_123456789_123456789_123456789_12
  my($p,$d,@l)=@_;$p=~s/_/[^@l]/g;$_=join''
  ,sort+map{split//}grep/$p/i&&s/[@l]//g,@$d
  ;$p=y;;;c;/(.)\1{$p}/&&return$1while--$p
}