I've never actually entered the Google Code Jam, and I rather suspect I'm not fast enough to compete at any non-trivial level. On the other hand, the questions are interesting algorithmic exercise, so I thought I'd have a go at a few of them.
Also, I've never really got super-proficient at the Java libraries. My day job, while working on Java, tends to mostly consist of maintaining and improving the code of others, which gives me surprisingly little opportunity at bashing out large chunks of code (although much more opportunity to exercise design...). Doing this kind of exercise gives me a chance to do some more interesting, self-contained exercises.
My aim here is to get the problems solved with an appropriate algorithm, and move on to the next one. This means the code lacks polish, explanatory comments, test cases (beyond those associated with the exercise itself), etc. This is not how I write production code! Don't judge me. :p