Monthly Archives: August 2016

Interview Questions: Types of Coding and Algorithm Questions

Part of a continuing series on Interviews and Interview Questions.

Today, we’re going to look at types of coding and algorithm questions. As discussed before, these can be divided up into ‘Problem Solving’ and ‘Knowledge’ questions.

As mentioned before, ‘Knowledge’ questions are very close to ‘human glossary’ questions. ‘What is the Big-O order of QuickSort? Average case? Worst case?’.

But there are some questions which straddle the line between knowledge and problem solving, answers that few but an expert in that topic would be able to exactly recall, like ‘what exactly happens between when you type into your browser and the page appears?’, or ‘compare and contrast various sorting algorithms’.

For those questions, you have to be as widely read as possible, they tend to select for those who are more naturally inquisitive for things outside their specific area of expertise.

Now, for coding questions. There seem to be a few different types, which I’ll try to separate out by data structure[1]:

Arrays and Strings – Any data structure where any element is addressable in O(1) time, where elements are allocated together in memory.

Linked Lists, Stacks, and Queues – Data structures in linear form, where elements far away from the origin are O(N) difficult to access.

Trees – Data structures arranged in a tree form, with a clear root and directionality. Often sorted.

Graphs – Data structures with nodes and edges, where the edges can connect the nodes in arbitrary ways. Home to at least the plurality of the known NP-Complete problems. Note that Graph problems are a superset of the above.

Search and Optimization – Problems where you’re trying to find an optimal (or close to optimal) solution in a large multidimensional tensor or vector field. Many in this category are easily mappable to Graph Theory questions, but many are not, such as 3-D Protein Structure Prediction. Most interviews would likely not ask questions in this category, at least not very complex ones.

Machine Learning and Statistics – Somewhat related to Search and Optimization, problems dealing with how one trains a computer to solve a problem. Likely to become more and more important.

Hashes – Data structures where space is traded for speed. Generally assumed to have 0(1) insertion and retrieval

[1]Hat tip:

Interview Questions: Other

In previous posts, I’ve talked about the most important types of interview questions:

‘Behavioural’ questions ask ‘Describe a time when you encountered a problem like this’.

‘Situational’ questions ask ‘Given this situation, how would you solve it?’

‘Technical’ questions ask ‘Solve this defined problem for me.’

Today, I’ll cover some other types of questions that are known to not have much predictive power, but people still ask, either as an ice breaker, or because they have other reasons for asking these questions.

‘Ice Breaker’ questions ask ‘tell me a story about yourself, to help relax you.’

The purpose of ‘Ice Breaker’ questions is to get the conversational flow started. My personal favourite is ‘tell me about the project you’re most proud of’, because it will help to relax the candidate, and has the dual purpose of showing what a candidate is like when they’re excited about something.

Dumb’ questions ask things outside the normal boundaries of a standard interview.

From the link, examples might include “What kind of animal would you like to be?” or “What color best describes you?[1]” The ostensible purpose is to try to get beyond pre-programmed/rehearsed answers, looking for original thoughts. (I tend to prefer the ‘tell me what you’re most proud of’ type of question, as if you’re trying to knock a person off their rehearsed interview game, if they’re nervous, that might torpedo them, and you’re torpedoing them based on their interview skills, rather than actual skills. Better to choose a topic they know, and explore the limits of their thinking there.)

‘Illegal’ questions ask ‘I want to discriminate against you, in some illegal way’

Which questions are illegal will vary by jurisdiction, but generally include questions about things such as gender, age, marital status, religion, etc… Larger and governmental organizations tend to be better at not asking such questions, whether because of visibility or lawsuits. Knowing how to answer such questions can be tricky, because of the power differential between interviewer and interviewee, but especially because the organizations asking such questions may be hiring from a labour pool with few options.

‘Brainteaser’ or ‘Fermi‘ questions ask ‘How many piano tuners are there in New York’?

These questions are the stereotypical ‘Google interview’ question, which is funny, because Google no longer asks this type of question[2]. I happen to enjoy this type of question, and they can be very useful for back-of-the-envelope estimation, but don’t really have a useful place in job interviews.

Next time, we’ll go more in dept about specific types of technical questions. Stay tuned!

[1]My favourite story on this topic comes from the brainstorming exercise: “List all the things you could do with this brick.” People would come up with some small number of ideas (like <10) for how to use the brick. Then the facilitator would say something like: "List me all the ways that your wackiest friend could use this brick." Interestingly, this generally elicits many more ideas, as it removes some of the social opprobrium of being 'weird'. [2]cf. The British Empire no longer uses the ‘Imperial’ system.