Tiny UID Algorithm generation

There are lots of url shortening websites but my very favorite is ir.pe
It's interface is clean and it's url is very short (5 chars if you count the dot).

I've been using the ir.pe service since it was created so i pretty much figured out how the uid where conceived. Here is the logic:

You start with a list of characters that you want to use. For example:

"abcdefghijklmnopqrstuvwxyz0123456789_-"

uids will be:

1 - a
2 - b
3 - c
...
39 - aa
40 - ab
41 - ac
...
78 - ba
79 - bb
80 - bc

And so on. Noticed the pattern?

Ok, if you are a developer take 10 minutes and try to create an algorithm that will generate those uids :)

-- Solution below, don't cheat! --

This algorithm needs to be fast!

I always add a new layer of complexity to this kind of exercise, the code needs to be not only fast but short. Fun Fun! (I'm a nerd, i know. You don't need to shout! :p

function generateCode(i:uint):String{
var s:String = "abcdefghijklmnopqrstuvwxyz0123456789_-";
return (i<s.length) ? s.charAt(i): arguments.callee((i/s.length)-1)+s.charAt(i%s.length);
}

It's ActionScript code if you wonder but the logic could be easily translated to a mysql/postresql/sql function (i recommend using a database function rather than a backend method creation).

In flash it takes 5871 ms to create 1 million uids and less than a ms to create 1.

Leave a comment with your own version!

--fernando