Most likely O^3

Oh, O(n^k) isn't so bad. Sure, it's a bit slow, but for reasonable values of n the process *will* finish. I presume this is only being run once per user, though n will be the number of users, which could be a bit on the high side. Still... might not be too bad. Computers are pretty fast these days.

OTOH, the other day I wrote a script that was horrible. I knew it was brute force when I wrote it, but I only needed to run it a couple of times, and n was never going to exceed 15 or so, so I didn't worry about efficiency. For n=3 it ran fine. Took a minute, but I knew it was an inefficient implementation. So I set n to 4...

Some of you may know where this is going. Windows Me told me I was running low on disk space, so I stopped the process and discovered that the swapfile was over 180GB. (It was a recursive algorithm...) So I analysed the algorithm, and it turned out that it was approximately O((n^2)!), and using an amount of RAM proportional to running time. Yeah, that's a factorial. Guess I have to come up with a slightly more clever algorithm.

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$;=sub{$/};@;=map{my($a,$b)=($_,$;);$;=sub{$a.$b->()}}
split//,".rekcah lreP rehtona tsuJ";$\=$ ;->();print$/
[download]

You might also wanna add a setup to require an email address. I know its not hard to have more than one email address, but add that with some form of email verification and it would make it harder to create duplicate accounts.

I can't see what you're proposing working well. Abusers are going to lie. It's trivial to find valid names and addresses with little effort. Tools like spamassasin work because it is hard to send, for example, spam about credit cards without mentioning the words "credit card". If there is no reason to input meaningful data then it's not going to work well. Dealing with false positives may also annoy your valid users.

Any ideas, and/or suggestions would be appreciated.

Depends on what business you're trying to run.

• One way of very quickly cutting down duplicates is to charge for registration.
• Another way is to use some piece of unique data that is hard to duplicate or make up. Credit card numbers come to mind (you don't have to charge them money - just check that it validates with the card company).
• Have a manual process. Have them have to appear in person to pickup login details. Have login details posted to their address.
• Although it is also easy to duplicate, making them give a valid email address is another mechanism that may help cut things down.

#!/usr/bin/perl
 
use warnings;
#use strict;
use DBI;

             my ( );
#put my vaiables ^ there
$testuserid=$ARGV[0];
$test_sql="select  firstname, lastname, password, username, dob, zipco
+de, age, remotehost, ut, secret_question, secret_answer from users wh
+ere userid=$testuserid;";
$db_test = DBI->connect("DBI:mysql:database=my_userdb;host=db_host","m
+aster","",{RaiseError=>0});
if ( !$db )
{        $fraud{$testuserid}->{secret_question}=$d->{"secret_question"
+};
        print "Cannot contact aladdin, bypassing.";
}
$query_test = $db_test->prepare($test_sql);
$query_test->execute();
while ($d = $query_test->fetchrow_hashref())
{
#       $testuserid=$d->{"testuserid"};
        $test4firstname=$d->{"firstname"};
        $test4lastname=$d->{"lastname"};
        $test4password->{password}=$d->{"password"};
        $test4username->{username}=$d->{"username"};
        $test4dob=$d->{"dob"};
        $test4zipcode=$d->{"zipcode"};
        $test4age=$d->{"age"};
        $test4remotehost=$d->{'remotehost'};
        $test4ut=$d->{"ut"}; #cookie
        $test4secret_q=$d->{"secret_question"};
        $test4secret_a=$d->{"secret_answer"};
        $fraud_factor=0;
# more queries, more variables
#...........................
#...........................
}
$db_test->disconnect();
$sql = "select userid, firstname, lastname, password, username, dob, z
+ipcode, age, remotehost, ut, secret_question, secret_answer from user
+s where status='ok' limit 5;";
$db = DBI->connect("DBI:mysql:database=my_userdb;host=mydbhost","maste
+r","",{RaiseError=>0});
if ( !$db )
{
        print "Cannot contact aladdin, bypassing.";
}
$count=0;
$query = $db->prepare($sql);
$query->execute();
while ($c = $query->fetchrow_hashref)
{
        $count++;
        $userid=$c->{"userid"};
        $firstname=$c->{"firstname"};
        $lastname=$c->{"lastname"};
        $password=$c->{"password"};
        $username=$c->{"username"};
        $dob=$c->{"dob"};
        $zipcode=$c->{"zipcode"};
        $age=$c->{"age"};
        $remotehost=$c->{'remotehost'};
        $ut=$c->{"ut"};
        $secret_q=$c->{"secret_question"};
        $secret_a=$c->{"secret_answer"};
# more queries, more variables
#...........................
#...........................
# do some creative tests, while incrementing
# fraud_factor for combinations of matches

}
$db->disconnect();
print "$testuserid\t $fraud_factor";
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