use strict;
use warnings;

my @str = qw(
	ABBCBCAAAAABBCBCACCCAAAAACAAAAABBBBBAAAAABBAAAAAAAABBCCCACCAABC
	BCCCBCAACAABBBCAAACCAAAAACAAAAABBBBBAAAAABBAAAAAAAABBCCCACCABBC
	ABCCBBBAAAABBABCACABCCCCCCAAAAABBCBBCCCCAAAAAAAAAAAAACCCACCACCC
);

foreach my $str ( @str ){
	
	print "$str\n", 
			$str =~ s/([A-C])(\1{2,})/$1.(1+length($2))/reg,
			"\n\n";
}

__END__
ABBCBCAAAAABBCBCACCCAAAAACAAAAABBBBBAAAAABBAAAAAAAABBCCCACCAABC
ABBCBCA5BBCBCAC3A5CA5B5A5BBA8BBC3ACCAABC

BCCCBCAACAABBBCAAACCAAAAACAAAAABBBBBAAAAABBAAAAAAAABBCCCACCABBC
BC3BCAACAAB3CA3CCA5CA5B5A5BBA8BBC3ACCABBC

ABCCBBBAAAABBABCACABCCCCCCAAAAABBCBBCCCCAAAAAAAAAAAAACCCACCACCC
ABCCB3A4BBABCACABC6A5BBCBBC4A13C3ACCAC3