Five Killer Coding Challenge Interview Questions and Their Answers
You’ve found a role that seems a great fit and passed the code challenge. Now it’s time for the interview.
Over the years, the management team at Geektastic has hired hundreds of developers. In that time we’ve found there are certain types of interview questions that will get discussions going and allow a skilled interviewing team to see how much you really know and how you might fit in.
If you’re a developer looking to prepare for your next interview, please take a few minutes out of your busy day and look at the killer questions we’ve compiled. Getting familiar with what you’ll be asked (and what to ask) can go a long way in helping you have a successful technical assessment in your job interview.
The five questions you’ll be asked at a coding interview
- Why did you make decision X in your code challenge submission?
- What happens between you typing a URL into your browser address bar, hitting enter and seeing a web page?
- What are the things you should consider if you were writing your own database server?
- How does role Y fit in with role Z within the development team?
- What environment are you looking for?
And here is how you should answer them:
1. Why did you make decision X in your code challenge submission?
The very fact you’re interviewing face-to-face means you passed the code challenge; the next step is to make sure you’ve come prepared with a rationale for the decisions you made and be ready to talk them through.
“Oh, I wrote that? I don’t remember”, could lead to some awkward moments. While it’s unlikely you’ll be expected to write out perfect code on a whiteboard (many developers use IDEs, and this is a reasonable mitigation for imperfect syntax), being able to justify your choices and the ability to rationalise and compare alternative solutions is particularly important in agile development teams.
2. What happens between you typing a URL into your browser address bar, hitting enter and seeing a web page?
An example of a broad type of question that could lead in any direction. You can talk about all sorts of things: maybe DNS to start with – what are DNS servers?/ How do they work at a high level or a lower level? Lookups. Primary and Secondary servers. Caching. TTLs. Change propagation. DNS records. A records. CNAMEs. MX records. And that’s just DNS. We’ve not hit a load balancer or web server or app server yet.
Although “there is a DNS lookup that tells the browser the IP address of the server that will respond to this request” is a good starting point, skilful interviewers might lead you down one or two rabbit holes to see whether you know more than the bullet points. Thirty seconds into your response you might be onto TCP, HTTP, transport layers, SSL, certificate chains – who knows?
You’re not expected to be Google and if the role involves building JavaScript libraries, a gap (or abyss) in your knowledge of transport layers is likely not going to kill your chances, but it’s always good to show that you know there’s more going on than just how much of the internet npm downloads when you build that 50 line JS file you’ve just written.
If you are a JavaScript engineer working on client-side code, it would not be unreasonable to expect that you have some depth to your understanding of how a web browser works – since that’s effectively the platform that you’re writing your code for.
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3. What are the things you should consider if you were writing your own database server?
Most software engineers, particularly those working with backend applications, will use data stores. But do you understand something more about the application underlying that nice GUI interface that you double click on? How would you write an application like MySQL or MongoDB or Neo4j?
Questions like these could lead into general database principles such as ACID; SQL / NoSQL; different types of NoSQL; transactions; logging; file storage; blocking/non-blocking I/O; threading; indexing; sharding; query optimisers etc.
As with question two, the interviewer is asking an open-ended question to investigate the bounds of your knowledge.
4. How does role Y fit in with role Z within the development team?
Many developer interviews will involve meeting lots of members of the team – in start-ups especially it’s not unusual to meet upwards of eight different people, all keen to check that you understand how your work will influence their work and how you’ll work together.
Do your research, spend some time before the interview thinking about how the IT flow works in the company and demonstrate you have an idea of how the pieces fit together with you there.
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5. What environment are you looking for?
Hopefully, you’ve done some research, and you know the company only has ten employees or it has a development team of 150. If you’re moving from large to small, or vice versa, it’s probably good to show that you know what you might be in for.
If you like a nice subsidised canteen and powering your machine down at 5:30 pm, then a ten employee company might not be for you. Be prepared to talk about the environment you’re expecting and how environments you’ve experienced in the past have worked. How do you see yourself fitting in? Do you understand how IT projects tend to work in smaller or larger development teams?
If interviewing at a startup, don’t make the mistake of thinking there are no rules. All smart businesses, no matter how laid-back and new, will want you to adhere to certain principles and take responsibility for your choices. Similarly, a financial institution, for example, will be looking for you to show you can follow strict protocols and understand how the work you’re doing is often directly quantifiable in financial terms for the business.
Some bonus tips for a coding interview:
● Be curious about the technology choices they’ve made at the company. If they’re not explained to you, ask about them and don’t be afraid to question choices particularly if there are apparent alternatives.
● If you’re not an expert on the subject matter of the role you’re interviewing for, it’s fine to say you’re interested in the technical challenges –make sure you’ve thought about what those might be!
● Don’t panic if you get the “how would you write a database server” question! Unless your interview is with a company that writes database servers, what is being assessed is your understanding of the nature of the problem and how you might approach it, rather than writing code.
● And it goes without saying, it’s usually a bad idea to lead discussions into areas that you don’t know much about. Suggesting you know Python if you’ve only copied and pasted the Hello World example can go very badly wrong. One of the interviewers might have hidden expertise in an area that only comes out in interviews! One-upmanship is a character trait that is not exactly a rarity in developer interviews, and if you’re starting from the Hello World position it’s best to come clean sooner rather than later.
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