## Sunday, April 19, 2020

### Google Code Jam 2020 in Lisp—Round 1B

Although I had quite a bit of trouble surviving this year's qualification round, I was allowed to participate in online round 1, which, as usual, is held as three different sub-rounds to accommodate participants from various time zones.  The first (1A) was in the middle of the night in my time zone, so I skipped it and didn't even get around to reading the problems.  But today I attempted  round 1B.  The problems were again very cute and interesting, and while I struggled with the limited time, I ended up being quite satisfied, even though I missed qualification this time.

### Problem 1: Expogo

I wrote a relatively simple implementation using search with memoization (caching) and a bit of pruning of implausible search regions, and that was sufficient for all three data sets.  According to the after-round summary, there's also a constructive solution.  I had suspected so, but couldn't find it.

### Problem 2: Blindfolded Bullseye

This is a nice search problem that involves some geometry.  I think I started with a reasonable search strategy, but then ran out of time when it came to doing the geometry... So I gave up trying to find a "good" solution, and coded the trivial brute-force solution for solving the easiest data set.  That was worth only 3 points, but those 3 points improved my final ranking by more than 1'000.

### Problem 3: Join the Ranks

This didn't look too impossible, but given the high amounts of points awarded for this, I suspected that this would be beyond my skills and decided to focus on the other two problems.

### Conclusion

With a full solution for problem 1, a half(?)-done good solution for problem 2, and the few extra points for the trivial data set of problem 2, I finally ranked #1996 [edited for final result].  As only the first 1500 contestants qualify for round 2, this was not sufficient.  But I'm quite happy with how it went, and am looking forward to round 1C, about two weeks from now.  And unlike during the qualification round, I didn't run into any issues with coding in Lisp—even though I haven't been using it professionally for several years now.