Hey there, better late than never.

The HW asks you to

Modify add_to_index so that a given
url is only included once in the url
list for a keyword, no matter how many
times that keyword appears.

So, where before when we added a keyword, we might get duplicate URLs in list that is returned because we never looked to see if the url we are adding is already associated with that keyword. You might play with the original code to see that happen. Now you want to change it so that the url just appears once for that keyword.

So yea, if you found the keyword, is the url already in that list? What will you do if is it?

http://www.udacity-forums.com/cs101/questions/38276/homework-47-test-cases these test cases will work for 4.6 too..just avoid calling record_user_click() proc

You need to make sure that for every keyword, each URL is present at most once, i.e. no keyword has the same URL twice. You need to achieve this by changing the procedure that adds a url to a keyword.

In 4.6 U have to see if a given url is present in the index for that keyword. If its already there then you should not add it.

[[udacity,["http://www.udacity.com/cs101x/index.html","http://www.udacity.com/cs101x/index.html"]] if you see in the above case keyword "udacity" already has "http://www.udacity.com/cs101x/index.html" url so you should not add the same url again.

I think the key to this problem is to create a nest set of for loops which first look through the keywords, then look through the urls. If the keyword and the url match, you can return out of the procedure without changing anything. If a match is not found you need to either add the keyword and the url or add the url to the existing keyword, using the append operation in either case.