It's harder to make a mistake in Java

It's harder to make a mistake in Java!
http://www.theregister.co.uk/2011/03/12/facebook_hacker_cup_kicks_off/

I'd love to know where to start with these problems! I don't feel like I have skills to design the required algorithm  - having a look at the solutions, they're not overly long. Will have to read them in more detail when I have time.