Tuesday, 5 December 2006

KISS (or why MS CS students have a bad time in interviews ...)

It's that time of the year when Master's students are hunting for jobs in China and we are flooded with resumes from students with Masters of Science in Computer Science (MScCS). We've spent the last couple of weekends interviewing the candidates that passed the front interviews and it has not been pretty. In fact, it has been pretty sad.

The biggest problem we encounter with MScCS grads is made very apparent in how they approach one of the our typical programming problems. This particular problem is fairly simple and with a little bit of thought, can be made into a linear (computer performs x more calculations for every element added to n, where x is a constant number) or O(n) type of equation. Most competent people will come up with a O(n^2) algorithm (computer performs n operations for every additional element added to n, resulting in rapidly increasing number of calculations per element added) to it at first, then after a little thought, realize that there are a lot of duplicated operations, refactor that out and come up with the linear solution.

MScCS are a little different - almost all the ones we have interviewed to date encountered this problem, probably came up with the O(n^2) equation ... then went off the deep end. They would inevitably come up with complex, fancy algorithms that utterly failed to solve the problem. These fancy algorithms would often handle the common case but fail on the boundary cases. They were fragile, easily tricked or prone to failure. When these flaws were pointed out, these candidates would come up with even more complex algorithms or add a lot more if/else checks ... resulting in even more brittle and unreliable code. None of them, if unaided, could come up with the ideal solution.

Well, that's not really true. One particular candidate, after coming up with 4 complex, unworkable algorithms, finally said, "well, since you have given me such a tight time limit, I have no choice but to brute force it." He then proceeded to give the ideal solution. Linear time, handles all boundary cases. But he would rather give 4 non-working solutions rather than the working, "inelegant" solution.

What I find strange and rather disturbing about these interviews is that it is somehow related to the mindset of those who are doing their MScCS. Bachelor level grads or people with several years of working experience rarely make this mistake. They either do it right or not at all. Yet for some strange reason, the MScCS students seem to value fancy algorithms over _working_ algorithms.

Maybe it's the MScCS curriculum here in China which tries to focus on fancy algorithms. Maybe it's just that the MScCS feel the need to prove that their abilities are above the norm for CS graduates. Maybe we just have incredibly bad luck with our candidates. Whatever the reason, extremely few MScCS fresh grads have passed our interviews. As you can imagine, in a production environment, we highly value working code and eschew the fancy algorithms, especially algorithms that needlessly complex. Simplicity and correctness is far more important in our craft.

The famous quote attributed to Brian Kernigham comes to mind:

"Everyone knows that debugging is twice as hard as writing a program in the first place. So if you're as clever as you can be when you write it, how will you ever debug it?"

When writing algorithms, another quote from Agile development comes to mind - "do the simplest thing that can possibly work." Keep It Simple ... er, let's call it Keep It Stupidly Simple (KISS) and avoid insulting anyone :)

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