Generate rand7 from rand5

Initially i though this problem is easy.But it is little difficult.

How to generate rand7() from the given rand5() menthod?

rand7 will generate random numbers between 1..7
rand5 will generate random numbers between 1..5

Url shortener

Write a URL shortner (like tinyurl) . Take a URL as input & return a shortened URL. If you use any kind of storage or persistence, please use the appropriate api's of the language. Another requirement is that we want to make our URLs as different as possible, so that successive calls return very different URIs
This is to ensure that small typo errors do not lead to users getting to a valid URL, but rather throwing up an error page.