title: How do URL shortener calculate the URL key? How do they work?
body: <p>How do <a href="http://en.wikipedia.org/wiki/URL_shortening" rel="noreferrer">URL shortener's</a> like <a href="http://bit.ly/" rel="noreferrer">bit.ly</a>  calculate a random key for each link? What algorithm would I need to know to create my own?</p>