Whiteboard coding interviews have their place too

People don’t like whiteboard coding interviews for a variety of reasons:

• they are hard;
• they are stressful;
• they are not representative of actual work;
• they can require very specific insight;
• there is no help available from an IDE, a textbook or Stack Overflow;
• one can revise for questions that are very similar;
• and many more…

I’ve done many whiteboard coding interviews at places like Google, Facebook and Palantir, and many other similar online tests also.

I believe the whiteboard coding interview has a valid place in the interview stack of some companies. Candidates should not fear it as much as many do. I’d like to outline my rationale below.

Why interview?

Hiring is a classification problem, and interviewing is one part of the classifier. The outputs are “should hire” and “shouldn’t hire”.

Like all classification problems, in hiring one must make a tradeoff between precision and recall, between false positives (hiring someone who shouldn’t be hired) and false negatives (not hiring someone who should be hired).

It is trivial to design hiring processes that minimise false positives (hire no one) or that minimise false negatives (hire everyone).

In practice, there are many types of hiring processes that appear:

• Take-home technical tasks
• Quizzes
• Chatting about previous work
• Questions about systems design
• Pair programming
• Open-source code contributions

All these hiring processes make tradeoffs between precision and recall. How do whiteboard coding interviews make that tradeoff?

Why whiteboard coding?

Whiteboard coding interviews are one of the better methods of preventing false positives: it is very difficult to pass the interview if you aren’t capable of doing the job.

Google, Facebook and others rely on whiteboard coding interviews for this reason: they want to avoid bad hires.

They do this even if it means they miss out on good hires. And they do. In 2009, Facebook rejected a candidate called Brian Acton. In 2014, they bought his company, WhatsApp, for $19bn.

Companies like Google and Facebook can afford to miss out on some good hires, because of the quantity and quality of the applications they get.

If you are a smaller company, or one that doesn’t get the quantity or quality of applications that the likes of Google or Facebook get, you are in a more difficult position. Hiring the wrong person is bad, but so is missing out on the right person.

What to do about whiteboard coding

Don’t let whiteboard coding interviews put you off applying for a particular role. If they do successfully put you off, I’d argue they are doing their job correctly.

Practise

Whiteboard coding interviews, like any other technical interviews, can be practised. I’d argue that it would be a better use of time to practise whiteboard coding as opposed to e.g. behavioural questions.

Many sites like CareerCup, HackerRank and Sphere Online Judge post questions very similar to those asked in interviews. The questions often draw from a small set of Computer Science theory.