#!/usr/bin/perl

use warnings;
use strict;

while (<DATA>) {
  chomp;
  print "$_ -> ";
  m/(\w)\Z/;
  my $last = $1;
  if (s/($last{3,})\Z/$last$last/) {
    my $len = length($1)-2;
    print "$len -> $_\n";
  } else { print "\n" }
}

__DATA__
ACTGCTAGGGGGGG
TCAGCTAGCNA
ACTGSCGACAAAA
GTCTGAGTTATTT

##</code><code>##

ACTGCTAGGGGGGG -> 5 -> ACTGCTAGG
TCAGCTAGCNA -> 
ACTGSCGACAAAA -> 2 -> ACTGSCGACAA
GTCTGAGTTATTT -> 1 -> GTCTGAGTTATT