DB<129> push @a, join "",a..z,rand(1) for 1..1e6
 => ""

  DB<130> $start=time;print lcp_v4(@a);time -$start
 => 1.25800704956055
abcdefghijklmnopqrstuvwxyz
  DB<131> $start=time;print lcp_v5(@a);time -$start
 => 6.93630909919739
abcdefghijklmnopqrstuvwxyz