Finding the intersection between two regexes

[Michael Lush]

On Tue, Apr 22, 2014 at 5:05 PM, Paul Makepeace <paulm at paulm.com> wrote:

> If your goal is to simply identify overlaps rather than generate
> encompassing regexes, you could try attacking it with
> intelligently/heuristically generated random numbers.
>
> Paul
>

Its just about possible to brute force the problem, on my box (~2.4GHz
intel)

my $count = 0;
foreach my $x (1..5000000000) {
    if ($x =~ /^246[2-9]\d{6}$/ and  $x =~
/^246(?:(?:2[346]|45|82)\d|25[0-4])\d{4}$/ ) {
        $count++;
    }
}
print "$count\n";

takes about 14 minutes to run,  it would be easy enough to parallelise the
search with threads
determine the minimum and maximum numbers that could match.  I guess you
could get the runtime
down to a minute or less.  Depends on how many regexes you have to evaluate