First Google Code Jam!

The format of this competition, allowing us to run programs on our own machines, brought up a very interesting issue for me: what programming language should I be using? (I had had similar considerations for IPSC 2013, but GCJ’s problems are closer to the traditional ACM-ICPC style.)

The obvious choice is C++, the language I use for roughly every other competition, but its safety (or lack thereof) is not very appealing. I need speed, but not that much speed. Unfortunately I still haven’t gotten around to learning any other friendlier mid-level languages (on the list: D, Go, or Rust), so I have no close substitutes for C++ right now.

Python is certainly available for a reliable arbitrary-length integer type, if nothing else.

As for non-candidates, Java has BigInteger and memory safety, but all in all I decided the benefits are too minor and it’s too ugly without operator overloading. Scala is probably way too slow. So I don’t expect to be writing either language.

The only difficult choice I have to make is, of course, Haskell — which can be quite fast, even while it’s ridiculously type-safe and expressive and referentially transparent and easy to reason about, once you’ve:

• figured out how to do the problem
• scrapped step 1 and actually figured out how to do the problem functionally
• gotten the thing to compile

Even if I can handle step 1, step 2 is by no means a simple task, as my struggle to implement a mere Sieve of Eratosthenes efficiently shows. That is fun, but not at all intuitive; I am doubtful I can do this under contest conditions. It is extremely difficult to transfer my skills in learning how to implement, say, a segment tree or treap into this language.

But! Google links to the programming language breakdown for 2010 Qualification Round as an example, and much to my surprise, Haskell ranks somewhere between sixth and tenth place in popularity (depending on what you sort by), so there are functional superprogrammers who can presumably do something like this.

As it happens, I ended up implementing all four solutions to the qualification rounds in Haskell, because of the relaxed time limit and lack of any involved algorithms and data structures. I think it was worth it.

Random video! Although I feel that I’ve heard it earlier, my first conscious memory of getting linked to it is from this post. At first I thought it would be the right background music for this post, but upon further reflection I think it mainly suited me while I was writing this post. Well, it’s topical if you mentally replace “day” with “year”.

Anyway. Around this time a year ago, I paused my participation in big high-school competitions, for a variety of reasons.

Firstly, I stopped attempting to make IMO both because I wouldn’t get that much from the training and because other people ought to have the opportunity. I was concerned that I might condition myself to only be able to do math with the short-term motivation of contests. Better to focus on college math and maybe some original research, I thought. During the year, I did lots of the former and very little of the latter. Meh.

As for the IOI, my obvious next target: I was tired of training and going abroad while paranoid about whether my immune system would hold up. I didn’t feel that the IOI was worth that. To some degree, I also felt burned out about programming. Long story short, my treatment should end soon, and learning Haskell completely resolved the burnout problem.

But the most important reason, I think, was that “high school was too short”. I started math competitions ridiculously early and didn’t spend much time exploring other interests. I thought I knew myself well enough that I could say I didn’t have many more interests at all, but I was completely wrong (psych nerds will reflexively note this to be the Dunning-Kruger effect). I coded lots in weird languages — Haskell, as mentioned previously, plus Scala, plus all manner of other magical command line tools. I wrote my first math problem and submitted it officially, picked up a new instrument, went to a debate competition, served as an unimportant tech guy for MUN, discovered and became hooked on Pentatonix, participated in three puzzle hunts in Australia and one in Massachusetts, figured out my rough political stance, rode a boat, got retweeted by @eevee and @Kyrgyzstan_News, increased my Neopets™ fortune by over 3400%, and lurked on FurAffinity a little too much.

But now, dear competition world, I’m back.

Funny, I go on a trip to Penghu followed by a four-day science camp and also get dragged into drawing classes and some sort of movie advising joint, and this is what I decide to blog about.

Since it’s summer, I went back to Rankk and solved stuff. This is lots of fun if you’re good with computers, plus a little math, cryptography, and general puzzling. I’m still stuck on level 8… oh well. Since the levels didn’t seem very indicative of difficulty to me, I decided to do some analysis.

New challenges have been added to Rankk over time, so my metric of difficulty is the number of solvers divided by the time from release to now. Of course this is far from perfect; for example, a challenge’s author doesn’t always seem consistently counted as a solver, problems with lower numbers and problems that will help level up are more likely to get checked out by new rankkers, and so on. But this is just for fun.

“I have been told that any encryption becomes safer if the underlying algorithm is maximally obscured, what is most conveniently done by coding it in Haskell.” – rankk

Functional programming is terribly addicting! Partly I think the completely different way of thinking makes it feel like learning programming, and falling in love with it, all over again. Partly there’s this evil sense of satisfaction from using $s (and later <$>s and =<<s and &&&s) to improve readability for initiated Haskellers and worsen it for everybody else. Partly it’s because Learn You a Haskell for Great Good! is such a fun read — there are too many funny bits to list but my favorite so far is when the author analyzes the first verse of Avril Lavigne’s Girlfriend.

Although I think my code in Haskell tends to be more readable than in other languages, code obfuscation in Haskell is almost natural: all you have to do is refactor the wrong function to be “pointfree”, which means that even though it’s a function that takes arguments, you define it without parameters by manipulating and joining a bunch of other functions. Example (plus a few other tiny obfuscations):

isPrime = liftA2 (&&) (liftA2 ($) (all . ((.) (0 /=)) . rem) (flip
    takeWhile [2..] . (flip (.) $ liftA2 (*) id id) . (>=))) ((<) 1)

QQ wordpress why no Haskell highlighting (Editor’s note from 2017: The migration should highlight this now!)

Also, for some reason, you can do this in Haskell:

ghci> let 2 + 2 = 5 in 2 + 2
5

(via Haskell for the Evil Genius)

Okay, but seriously now. I wrote this about my journey to learn functional programming in the programming babble post half a year ago:

The main obstacle I have is that it’s hard to optimize or get asymptotics when computation is expensive (a big problem if you’re trying to learn through Project Euler problems, particularly ones with lots of primes).

because my title needs to mean something. (note from the future: before late 2017, when I migrated to Hugo and GitHub Pages, the blog was called “BetaWorldProblems”.)

Google just announced it’s shutting down Google Reader in three and a half months… I am participating in the friendly Reddit DDoS-hug of all the alternatives (list, but scroll around in the thread for a few more). Darn.

So, what have I been doing with programming recently?

Scala is an amazing multiparadigm programming language that runs on the Java Virtual Machine and interoperates with Java. I learned about it last time reading random articles on Twitter.

When I say “amazing” I mean “This is a language in which my code gives me nerdgasms every time I read it.” Wheeee.

Okay, it’s not perfect. People say it’s too academic. It has a notoriously complicated type system (which is Turing-Complete at compile time). Its documentation is a bit patchy too. For a serious introduction, the Scala website has plenty of links under documentation, and a tour of features. Somebody wrote another tour that explains things a bit more. So here, instead of introducing it seriously, I’m just going to screw with its features.

Example of freedom. Scala lets names consist of symbols, and treats one-parameter methods and infix operators exactly the same. The full tokenization rules are a bit detailed and I put them at the bottom of this post for the interested. This lets you create classes with arithmetic and domain-specific languages easily, but it also creates some silly opportunities:

scala> val * = 12
*: Int = 12

scala> * * * * *
res0: Int = 1728

Okay I don’t actually know how this pointless rambling got so long. I know the longer it is the more people will just tend to skim, because I do that all the time. So I went back and refactored—er, rewrote all the somewhat tangential bits (wow these puns are too easy) into footnotes. Manually. Obviously if I have to do this again I’ll write a script for it. But the post is still really long, and I bet nobody will read the whole thing. Oh well.

Life updates: I got out of the hospital Friday two-and-a-half weeks ago, went to the preliminaries of NPSC (a national team programming contest) with classmates, threw up a lot, went back into the hospital, and came out again. I wrote a lot of stuff about the experience and how much it sucked (hint: a lot) when I started this draft around that time, but now putting so much detail in this post feels weird. I’m mostly good now.

Three years ago NPSC was the only programming contest I really knew of; now I’ve participated in quite a few more, both online and locally, but it’s still the only contest I’ve entered that gives you real-time verdicts. I believe it inherits this from being modeled after ACM-ICPC, but that’s for college people and I’m less clear on how it works. All the other contests, namely TopCoder, CodeForces, USACO, and the other local individual competition (there doesn’t appear to be an English name so for the purpose of this post I’ll just call it “Nameless Local”; there’s a nation-wide competition in one-and-a-half weeks!), have system tests after the contest that don’t allow you to resubmit afterwards.¹ They all give pretests that you get to know about right away, just to catch super-silly non-algorithmic mistakes like failing to remove the debug statements or reading input from the wrong place, but these contain weak test cases and don’t guarantee that the solution will pass the system tests and get full score.