Monthly Archives: April 2013

How to impress me in a coding interview

At Square, candidates are expected to actually write code during the interview process – on a computer, not on a whiteboard. As a competent software developer, this kind of interview should feel like a gift. Your skills are going to be measured more or less directly by doing the very thing you’ve been doing all these years!

So how do you impress me – or any interviewer – in a coding interview? Here are a few things I consider when pairing with a candidate.

It’s about the process

First off, let’s deal with a myth: the interview is not about the answer to my question. Sure, I’d prefer that you get it right, but I’m far more interested in seeing how you work to get there. I want to see how you decompose problems, conceive solutions, and debug issues as they arise. Make sure you take the time to show me how you’re getting to the answer.

It’s about communication

A big part of the development process on a healthy team is communication. Ideally I’d like to leave the interview feeling like you’re someone who asks good questions and is receptive to feedback and external insights. A great way to blow this portion of the interview is to hunch over a notepad and scribble quietly while I wait. If you must do something like this, be prepared to explain your thoughts thoroughly when you’re done.

Don’t go it alone

My interview exercise is hard. I fully expect that you might need a hint at some point. I even enjoy working with you to debug the problems you hit as you work. But if you never ask, you’re not going to come out ahead. Coding on a real team often involves working on something that you don’t understand, but that the person sitting two seats down knows in detail. You should be self-sufficient only insofar as it makes you productive; spinning your wheels trying to go it alone is just indulgence.

You should run the interview

Don’t make me march you through all the steps. Once I’ve explained the exercise and you’ve started coding, it’s best if you drive. If you need help, ask. If you think you’re done, propose more test cases or ask for my thoughts. The best interviews I’ve had are more like working with the candidate than interviewing them. If you can do this in an interview setting, then I can believe you’ll work the same way when you’re on my team.

Use the tools

I am consistently impressed when a candidate is able to drop into a debugger or quickly access documentation in the IDE of their choice. It’s an aspect of professional mastery that will be extremely important to your day to day productivity. The inverse is also true – if you choose to write C++ in vim and don’t know how to save the file, it’s going to cost you.

No bonus points for doing things the hard way

One of the key attributes I select for in coworkers is pragmatism. Sometimes this means choosing an ugly but expedient solution instead of an elegant but expensive alternative. If you know when to make these tradeoffs, you’re someone I want to work with. A lot of candidates feel pressure to give me “perfect” solutions right away, but I’d rather see an answer than an incomplete, perfect one. Plus, I love it when we can iterate on the “quick and dirty” solution to build a refined version. This is how software works in the real world, and I love when candidates aren’t too self-aware to just go about it casually.

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