URL problem

bAAGi

Problem:

Subdomain names can contain an underscore, but domain names cannot. How can you allow for the subdomain to contain an underscore, but not allow for one in the domain? Also, you must allow for more than one subdomain.

Allowable:

[url]http://a_1.b.c.1234.com[/url]
[url]http://a.b_1.c.1234.co.uk[/url]
[url]http://a.b.c_1.1234.com.au[/url]
[url]http://a_1.b.c.1234.info.au[/url]

Not allowable:

[url]http://a_1.b.c.1_234.com[/url]
[url]http://a.b_1.c.12_34.co.uk[/url]
[url]http://a.b.c_1.123_4.com.au[/url]
[url]http://a_1.b.c.1_234.info.au[/url]

Weedpacket

I guess you look at the last part. If it's three or more characters long, make sure there are no underscores in it or the second-to-last part. If it's two characters long, make sure that there are no underscores in it, the second-to-last part, or the third-to-last part.

Gee, that avatar looks familiar...

bAAGi

There's a problem with that solution. How do you tell what is the subdomain and the domain, and what is still the TLD?

http://123.abc.com

http://123.abc.com.au

http://123.abc.nl

Go back one in the first and you're in the domain, but in the second, you're still in the TLD. If you check the length of the TLD, and go back two if the length is two, you end up in the subdomain in the third.

The avatar is my favorite cartoon character ever.