I’ve been doing a round of interviews recently, trying to replace a contract that has recently come to an end and I’ve come to a conclusion – I’m really good at my job but I’m terrible at interviews!

Well, not all interviews. There are some interviews I’m great at. The ones where a real conversation can be had about a diverse range of topics and in which the answers can have some nuance to them. The kind of interviews where I feel I have come out knowing a bit more than I went in with regardless of which side of the table I’m sat. I like those interviews.

I hear you walk good. Let me tie your shoelaces together, blindfold you and spin you round a few times. Now show me your walk.

The kind of interviews I’m terrible at all have a very particular rhythm to them. The meeting starts, pleasantries are exchanged (mostly, although some technical interviewers I’ve met don’t even give their names) and everyone settles into their chairs. A sheet of paper and a pen are slid across the table. My heart sinks, this is going to be one of *those* interviews which have the very black and white questions.

Am I perhaps putting pride before a fall? Shouldn’t a candidate expect to jump through some hoops to get the job? Isn’t this all just good due diligence? Don’t most programming problems come down to boolean logic and therefore the answers can be deemed correct or not? Well no, I suspect that the only interview questions with objectively correct answer are the cases which are trivial. Those questions annoy me.

Question – “In C++, what is wrong with this reverse function?”

Answer – “It’s not std::reverse?”


Answer – “It’s in the global namespace?”

Correct Answer – “No! There is no test associated with it and there are loads of bugs!”

More Correct Answer – “Why did someone write all this codes and all these tests to bloat our code base with a worse version of the C++ Standard Library? Who do we employ who is better than Howard Hinnant and why aren’t they contributing pull requests to llvm?”

Question – “Write an algorithm to count all the pairs in an array, matching a predicate, the 2 test sets are 5 elements long… with permanent pen and a single side of A4!”

Answer – “Er… vaguely this? I usually hit F7 about now and run some tests while I have a little think about the wider structure (or it’s already been gulped).”

Correct Answer – “No! There’s a bug! And it uses O(n^2) complexity!”

Question – “How would you optimise it?”

Answer – “Er… does this code really need optimising? What’s the real world usage of this algorithm? How often does it get run? Is this ever going to have more than 5 values passed into it? If this is all we’re doing can’t we just go perfectly wide over all cores for every combination and accumulate to an atomic variable? Can I just Map-Reduce it? Use a GPGPU?”

Correct Answer – “No! This was a set of unique numbers! You could have optimised for that!”

“Er… nothing in the brief said this was guaranteed to be a set… why isn’t it sorted? Is this really all you ask people to find out if they’re worth giving a job to? Where are the architectural system design questions? How much did you say the hourly rate for this position was?”

Don’t you have infinite monkeys somewhere that can do this?

The older I get, the more these trivial pen and paper questions irritate me. I don’t go as far as to say all these things in the interview but I probably don’t hide my inner monologue very well.  I have had a fair number of jobs now and hired a fair few people myself, yet not a single one of those jobs started with someone giving me a permanent pen and paper coding test.

My Dad used to write code on punch cards. To compile it he had to catch a train to London. I write more lines of code per day than my Dad did.

We are all standing on the shoulders of giants. Alan Turing gave the world its greatest tool since the wheel and it is the height of arrogance to consider that any code is written in a bubble. If you are not assessing the capability of  your developers to write code in a meaningful environment, in context to other code and the data it transforms, then you are failing to do your due diligence and opening yourself up to immense risk.

Hiring is a two way process with the candidate trying to assess the quality of the development team just as much as the interviewer is trying to assess the quality of the candidate. The goal of an interview is to assess the depth and breadth of a candidate’s understanding and ability to apply principles in practice, not to find out how much someone enjoys toy puzzles.

So, hiring managers, I have one thing to ask. Next time you take the effort to look at a CV,  check the references and talk to a candidate on the phone. Don’t then call them in for a pen and paper test of the most trivial nature and waste their time and yours. And even if you change nothing else about your tests, at the very least give the candidate a text editor and a delete key and assess whether they can even type!

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