Results 1: http://dogs.com Result 2: http://www.dogs.com
These 2 aren't the same: one is the main domain, the other is a subdomain. There's no guarantee that they serve the same content.
What you're asking for is basically impossible: any part of the URL is important and changing it may result in a different page.
That said, there's a <meta>
tag for canonical
which indicates the normalized URL of a page. Only that URL is (somewhat) guaranteed to be correct.
Also, you could just pull the content from pages and compare them. But, again, no guarantees.