Monthly Archives: April 2012

Exercise Mania

My ex-girlfriend’s mom started doing a jazzercise class in the 80s and hasn’t stopped since. It’s a weird thing.

Programming exercises can be just as addictive as some forms of well-marketed physical exercise. I have to actively resist writing solutions in Lisp to every silly problem I stumble upon online. But this morning, I came across this simple one (a blog post from 2007, but that happens on Hacker News) and, for some reason, couldn’t pass it up:

Write a program that prints the numbers from 1 to 100. But for multiples of three print “Fizz” instead of the number and for the multiples of five print “Buzz”. For numbers which are multiples of both three and five print “FizzBuzz”.

It’s so silly that I guess some folks, like the blogger linked above, have turned it into a problem of “what’s the most creative/strange way I can think of to do this?” Which is interesting and fun in its own right.

What I don’t understand is the attitude expressed in the original fizzbuzz blog post, “Using FizzBuzz to Find Developers who Grok Coding”. Does it really matter if it takes someone 5 or 20 minutes to write a solution? (FWIW, I took about 10 mins). A shorter time with such a goofy example means someone “groks” coding more than another? Ridiculous.

These types of puzzles are amusing precisely because a lot of real-world development (which is what the vast majority of people who code for a living do) is unfortunately pretty rote, and doesn’t require a lot of algorithmic thinking. Code monkeys learn to use libraries and frameworks, and spend a lot of time trying to use them correctly and cleanly, in order to implement straightforward requirements. So these exercises are a shift in mindset. In a tiny way, they put you back on the path of engineering. It’s why people find them interesting to do. It’s why I’m reading the Structure and Interpretation of Computer Programs.

Taking a few more minutes might mean you’re not accustomed to solving such problems every minute of your working life. But that’s not at all the same as gauging whether someone understands coding or not. That kind of measurement is naive at best.

An SICP exercise in implementing cons, car, and cdr

I started working my way through the Structure and Interpretation of Computer Programs this week.

Contemporary “intro to programming concepts” texts tend to focus on real-world examples in areas like business and web-based applications. In contrast, SICP involves a lot of math problems. I’m liking this about the book. Math is particularly good for illustrating the difference between declarative and imperative knowledge, between “describing properties of things and describing how to do things.” You may know, formally, what a square root is, but coming up with a procedure for calculating the square root of a number is another matter. Bridging these two kinds of knowledge is the essence of what computer programming is about.

The second section, “Building Abstractions with Data,” starts by discussing different ways to implement an abstraction for rational numbers. The text walks through using a Lisp cons cell to store a numerator and denominator pair, and using car and cdr as selectors. Then it provides this exercise, which I found particularly intriguing:

Exercise 2.5. Show that we can represent pairs of nonnegative integers using only numbers and arithmetic operations if we represent the pair a and b as the integer that is the product 2a3b. Give the corresponding definitions of the procedures cons, car, and cdr.

That’s a really clever way to store a pair! But perhaps I only think so because I’m not a math person.

At any rate, I wrote a solution in Common Lisp, with some helper lambdas to calculate log and pow arithmetically.

I’m finding that thinking about math problems and learning Lisp are helping me think more algorithmically about solving problems in the code I write for work. Maybe I’m starting to experience what Eric S Raymond famously wrote about Lisp: that it “will make you a better programmer for the rest of your days, even if you never actually use Lisp itself a lot.” I’m holding out hope for that last part though…