Since web pages can have multiple URLs pointing to them, as a web browser developer how can you make sure you have never seen the same content before?  

 

Solutions:

 Make a list (or a binary tree) of hashes using MD5, SHA1 or a similar hash/digest algorithm of the pages you have visited. Then compare the digest of the current page to the hashes in the tree. A hash table is good here too! A hash table of other longer hashes is a quick, easy, and efficient solution.