use strict;
use warnings;

my @strs = (
    '010111',
    '0' x 1_000_000,
    '01' x 1_000_000,
    '011' x 1_000_000,
    ( '01' x 1_000_000 ) . '111',
);

for my $str (@strs) {
    my $len =
      ( () = $str =~ m{ 0+ | 1+ }xg ) +
      ( $str =~ m{ 000 | 111 | (.)\1 .* (.)\2 }x ? 2 : 0 );

    print $len, "\n";
}