While discussing other methods that avoided regular expressions in the CB with
bobf and
nothingmuch, I mentioned an unpack/hash solution.
nothinmuch asked to see it, so here is a highly untested alternative.
#!/usr/bin/perl
use strict;
use warnings;
print str_count('ABAABAAAA', 'AA'), "\n";
sub str_count {
my ($str, $pat) = @_;
my %substr;
my ($p_len, $s_len) = (length $pat, length $str);
my $template = ("A$p_len" . 'X' . ($p_len - 1)) x ($s_len - $p_len
+ + 1);
$substr{$_}++ for unpack $template, $str;
return $substr{$pat};
}