my ($correct, $incorrect) = 0;
for(0 .. length($string)-1) {
    if( substr($string, $_, 1) eq substr($guess, $_, 1) ) {
        $correct ++;

    } else {
        $incorrect ++;
    }
}
[download]

There's probably 600 ways to do it without regexes, but I think the only way you'll get a regex to work is with (?{ }) embedded code match thingies, and that's voodoo. I'm not saying it can't be done, but the documentation on them suggests you not use them.

Please see: perlre, for, substr.

I've read your question three times, and I don't have an answer, but I want to make sure I understand the question.

The data involved are:

1. A secret number
2. A guess at what the secret number is (e.g., 1122)
3. Some description of how the guess matches the secret number (e.g., two of the digits are in the secret number in the place that they were in the guess, and one of the digits is in the secret number but not in the place that it was in the guess).

What you want is a regular expression that will match every possible number that the secret number could be, given the data you have.

Additionally, you want to be able to add (1) another guess, and (2) more data about how that guess matches, and refine the regex further.

Is that correct?

Yes, exactly. You have put very nicely in words.

I have few more ways in mind. Based on the guess, it can generate set of numbers that matches the conditions. Example: (1122:2:1) can give the set: x112,1x12,12x2,122x. Later on I can combine the sets( cross product) to see, which combination works good ( instead of generating a possibly complex regexp)

--Artist

(1122:2:1) can give the set: x112,1x12,12x2,122x

There you have me totally confused. Take the second element from your set, 1x12. The two digits in their correct positions must be the first and last, no? So that means that the 1 in third position must exist in the target string, but at a different position than in the "guess" string.

Do you see the problem yet?

#!/usr/bin/env perl

use warnings;
use strict;

my $num_good = 2;
my $num_bad  = 1;

my $try;
my $target;

$target = 1122;
#$try    = 1232; # good
$try    = 2211; # bad

my @digits_targ = split //, $target;
my @digits_try  = split //, $try;

my $cnt_right = 0;
my $cnt_wrong = 0;
for my $i (0 .. $#digits_targ) {
    if ($digits_targ[$i] == $digits_try[$i]) {
        $cnt_right++;
    }
    else {
        $cnt_wrong++;
    }
}
#print "cnt_right=$cnt_right\n";
#print "cnt_wrong=$cnt_wrong\n";

if (($cnt_right == $num_good) and ($cnt_wrong >= $num_bad)) {
    print "good\n";
}
else {
    print "bad\n";
}
[download]

Update: I like jettero's use of length and substr better than my use of split.

Your logic has slight problem at

$cnt_wrong >= $num_bad
[download]

According to your code 9922 turns out to be 'good' but it should be 'bad'.
--Artist