Technical Interview Part 2


What I do instead

Before technical interview session, a technical assignment given to the candidate on Friday, so that they can work on it over the weekend. The technical assignment typically takes few hours to complete. I have a range of questions from demonstrating a design pattern, build a simple application with database interaction, to SEO analysis algorithm.

The objectives of the technical assignment are:

  1. Ensure the candidate can codes.
  2. Evaluate how modern his development approach (for example, whether the candidate will use Elmah or Log4Net over writing a custom logger class)
  3. Evaluate how serious he treats his codes (if a candidate deliver a half-hearted solution, it indicates the same for his work codes)
  4. Evaluate whether he goes the extra miles (such as implementing unit tests and proper exception handling)

During the technical interview, I will do the following:

  1. Have the candidate to explain the core of the solution. I will then ask a few questions base on his implementation. For example if I want to implement certain change, where should I modify the code. This is to ensure I’m talking to the person who wrote the codes.
  2. Find a flaw in the system and press on it again and again – in a professional and respectful manner. This is to evaluate how well the candidate respond to criticism, whether the candidate get defensive and whether the candidate is open to feedback.
  3. Challenge the candidate on how he can upgrade his solution to be production ready on both code and infrastructure level. This is to evaluate how much thought he has given to his solution and how much of exposure the candidate has dealing with production system.

Next, I will move on to a list of generic topic on software development. Example of the topics I cover.

Source Control

Every developer uses source control to certain extend. I will normally ask what kind of source control has the candidate use. The top 3 answers are TFS, Git and SVN. I will ask the candidate to share with me, what are the differences between the top 2 source controls he is familiar with. The idea here is to discuss about what the candidate is familiar with so that he can show his best thoughts. Depending on what the candidate bring up to the table, I will get a sense of what kind of developer the candidate is.

For example, if a candidate tells me checking out a branch in TFS is downloading a whole new copy of the code; while Git is merely applying the delta difference on the same copy of the code, it indicates this candidate used to work with giant code base with some level of branching experience and he appreciates Git is much more efficient on client side storage.

Another example, if the candidate brought up terms such as Rebase, I will follow up by asking what is the difference between Rebase and Merge on theoretical level and when is a good scenario to use Rebase over Merge on practical level. Depending on the scenario given, I might (or might not) have further question to validate the usages. The idea here is I’m following up on the topics suggested by the candidate himself. If a candidate cannot provide solid evidence on how familiar is he with the topic suggested by himself, that indicates the candidate is throwing fancy terms around hoping to impress the interviewer.

Design Pattern

Despite the challenges I highlighted earlier on design pattern, I still think design pattern is a good topic to cover during technical interview because the right application of design pattern indicate the complexity of codes the candidates has dealt with, hence the need of design pattern.

Ever since I take the role of being an interviewer, I do make it a point to read up on additional design patterns that I have never used. The good news is, most candidates consistently brought up only a handful of design pattern. The top 3 are such as Singleton, Abstract Factory and Repository.

Although Dependency Injection is not strictly a design pattern, a lot of candidates did mention Dependency Injection as something they know under the design pattern topic. I do not dismiss this answer just because it did not fit into the definition. My objective here is to assess the candidate’s ability to design his code structure, not a competition of giving definition.


What do I look out for during Design Pattern discussion? Take Singleton for example. After the candidate mentioned he knows Singleton, I will follow up with question “What is a good use case to use Singleton?”. The typical answer I got is something along the line “when you only need to have a single instance of the class”. Good. At this point, I know that the candidate is aware of the definition of Singleton although did not provide the use case I asked for. I will rephrase my question slightly differently to remind the candidate I’m looking for a use case.

One “interesting” answer always pop up is to apply Singleton in data layer (CRUD operation to database). I call this interesting because anyone who give a little more thoughts or have done some research in Singleton will realize it’s a bad idea to apply the pattern in data layer. However, this misconception comes up very frequently.

I will take this opportunity to explain to the candidate the kind of problem will surface for applying Singleton in data layer. Why do I do that? Having the right skill or information is important, but having the right attitude is equally (if not more) important. You can teach someone new skill but it is extremely challenging change someone’s attitude. At this point if the candidate appears to be enlighten with the new information, I know the candidate is coachable. In most situation, I would rather to have a coachable new hire (although not having the top notch skill set) over someone with superstar skill set but a poor attitude.


Working with database will come across a developer’s path very frequently. It is an unspoken rule that a developer must be able to work with database. With the amount of storage options in the market, it is difficult to discuss all of them but we will stick with the most popular option for most .NET developer – SQL Server in this article.

When hiring a junior developer, the candidate will have to prove his ability in writing T-SQL. Insert, Update, Delete and different kind of joins. No big deal. For senior developer, I would normally ask the candidate what other exposure does he has apart from T-SQL. Asking the actual involvement in SQL Server gives me very good indicator what kind of system the candidate has dealt with.

For example, if the candidate claimed he takes care of database backup, I will follow up with what is the backup cycle and types of back up he was using. If all the candidate did was doing a full back up on daily basis, it indicates the database size he was dealing with was not very large and the data lost does not seem like a big deal which means the data is not extremely critical.

If the candidate mentioned he scales SQL Server, I will follow up with what type of replication he applied and what is the rational behind the decision. I will also ask what other strategies he has considered before using replication because replication is an expensive option. If the candidate brought up Redis cache and index provider such as Solr or Azure Search, it shows the candidate has looked beyond SQL Server context which indicates he is someone having very broad skill set across technologies.

Once a candidate told me he implemented table partitioning in his database. I asked what is the logical condition he applied his partition base on. He said primary key which is GUID data type. That was an interesting answer because the generally approach to create partition is to base on date or some other logical conditions. I explained to him how I would implement table partitioning instead and the reason behind it. His eyes were brighten up.

Notice that I did not say “This is wrong. The correct way is this”. Instead, I make it as a discussion on “This is what I will do instead”. The same information was delivered across, but the outcome will be very different.

The candidate impressed me because he knows about table partitioning that most developer don’t. It suggests that the candidate is someone who took the extra effort to learn new skills to solve problems. Most importantly, the way he responded to the information I shared with him suggests he is someone coachable. I took this candidate into my team and he has proven to be a star team member.

Few final thoughts…

There are a lot of other topics that I cover during the interview. Most of them are generic topics such as tweaking software performance and security. The purpose of having a standardized list of topic is to ensure I use the similar benchmark for candidates for the same position. The reason to start with generic topic and drill further down is to allow the candidate to talk about areas that they are familiar with so that they can showcase their sharpest thoughts.

When candidate brought up certain topic for discussion, I’m assuming he knows about the topic very well. I’m handing over the power to drive the discussion to the candidate to certain extend. I prefer to talk about what the candidate is familiar with (instead of mine) so that I can truly assess his level of technical competency. Frankly, there is very little value to talk about a topic the candidate has only read an articles on 6 months ago. However, whichever topics that the candidate brought up, I will drill really deep to ensure he indeed knows about them rather than just throwing some fancy words around. 

During technical interview, I’m looking at more than just technical skills. Technical skills is learnable. What really interest me are:

  • Whether the candidate is coachable?
  • How big of passion the candidate has over technology?
  • What is the candidate’s approach in solving problems?
  • What is the candidate’s attitude dealing with technology and PEOPLE?
  • How much of potential the candidate has so that the company can groom him to be a superstar developer and beyond?

The technical topics I have for the candidate were merely for me to expose those areas I’m interested to learn about the candidate. I’m never interested to know the difference between a clustered index vs non-clustered index or the difference between Azure Web Job vs Azure Worker Role vs Azure Function. Given a laptop with internet, anyone can Google them in 5 seconds. What I am interested to discover is whether this candidate is coachable, his passion, his approach, his attitude and his potential!

Ideally, we should hire the right person with the right skill. However such angels rarely come by. If I have to choose between the right person or the right skill, I will choose the right person any day. Of course, provided the candidate still has reasonable level of skill set on the role he is applying. New skills are learnable and very often it is very quick to learn a new skill. Coaching a person takes a much more time, energy and cha-ching – if you are lucky.

If you are not lucky, a bad apple not only bring down productivity but also break the current harmonious team. It is much more effective to filter the potential troublemaker than to “coach” or “develop” him later. There is no point hiring bad apples just to hit headcount. With people, slow is fast.

Some companies practice having a couple strong technical guys to interview candidates whom they might not eventually work with. The interviewers are hiring for the company wide. Some companies practice having the Team Lead / Architect within the team to interview the candidates whom they will eventually work with. They are hiring for the team. I have been in both the situations and personally I prefer to the latter.

Being able to work with the person whom I interviewed earlier will give me additional consideration and deeper thoughts into whether the candidate will be a good fit into my team. Another good reason is to allow me to validate and refine my interview techniques. Interview is all about perception and assumption made on the candidate. I have made good decisions and I have made bad decisions. However, in the situation where I made a wrong assumption base on a wrong perception, I can adjust my interview technique on a continuous basis if I have first hand experience working with the candidate I interviewed.

Finally, I don’t claim what I’m doing is the only way or the best way. We live and we learn 🙂 I found this approach to be working quite well hence I continue practicing. If you have any thought on this, please leave me a comment. Hope you have found something useful in this article. Until next time. Cheers!

Technical Interview Part 1


Technical interview is both an exciting and stressful moment. It is exciting because there is a potential career opportunity ahead of you. It is stressful because you subconsciously aware that the people in the room are there to judge you.

I have been on the both side of the table – being an interviewer and an interviewee. It is stressful to be an interviewee for obvious reason. We need to try hard to sell ourselves and “sales” is not a skill that come naturally to technical people like us. Furthermore, you never know what kind of psychopath you might meet, asking you to find a bug in his rocket science algorithm. It is equally stressful to be an interviewer. Now your shoulder carries the responsibility of evaluating a candidate whether the candidate will be a right fit to the organization for long term. Being too lenient, you might get a bad apple into the existing harmonious team; being too strict, you might lose a black horse who might just need a little polishing.

As an interviewee

Let’s deal with the stressful problem for the interviewee first. Throughout my experience, I noticed I perform best when I’m not feeling nervous. The key to not feeling nervous is not to feel desperate for a job. Always look for a new job when you least needed it. When you don’t “need” the job, you are going into the interview room as an equal. Low need, high power and vice versa. Did you notice the term interview basically means “viewing each other”. You go in as an equal to evaluate the company as much as the company is evaluating you. The outcome of having this mentality allow you to feel more confident. Again, from my personal experience when I go into a technical interview with this mindset, I often have a pleasant technical discussion with the interviewer.

As an interviewer

Now for the interviewer. I’m not sure how many interviewer will feel stressful. I did not feel being an interviewer is a stressful task until I’m conducting interview for the 3rd year. Interviewee will usually be polite and humble. Most of the time, interviewee will do their best not to offend or make it difficult for the interviewer. I always felt I have an upper hand while conducting interview, hence I never thought there was a problem. It was only until I pull myself out of the technical interviewer’s role and give a more holistic insight from the organization perspective. I realized there are so many other aspects I need to put into consideration while conducting technical interview.

For example, during one interview I found out that talking to me in a technical interview is the 7th round of interview the candidate has gone through. He has taken online technical test and other technical interviews prior to talking to me. My final feedback on the candidate is a clear ‘No’. However, that got me thinking how and why did the candidate was able to pass the previous 6 rounds of interview but not my technical interview. Is there something wrong with the way I asked technical questions? Or does it simply means the previous 6 rounds of interview were not done effectively?

Another example, the organization has an expansion plan is to grow another 100 headcount in 1.5 year. That is equivalent to approximately 6 new hires in a month. Aggressive? Definitely! However base on the current hiring rate, we will not be able to hit the number. What need to be done differently? Should I lower my technical benchmark? Should I say we can’t meet this number simply because we cannot find the talents? How big (or small) the impact is to the projects if we do not meet the numbers? Most importantly, where should I find the balance?

The nature of software development skill set has both breadth and depth. Ideally it will be perfect to pair an interviewer and interviewee who have the identical technical domain experience. Reality is due to the today’s technology breadth, developers often focus on very different vertical skill set. For example, the interviewer might be an expert in Azure Web WebJob, Azure Storage and MVC but the interviewee has been working on Angular, Web API and SQL Server. Both of them are expert in their respective full-stack domain but there is very little common ground.

Let’s face it, both the interviewer and interviewee would not know every topics in great depth, even just within the Microsoft stack of technologies. How can the technical interview being conducted in a fruitful manner with this breadth and depth nature? Do I dismiss a candidate just because they don’t share the similar background with me even though he is talented, passionate and willing to learn?

What is the solution? Should the interviewer ask something more generic and academic like object-oriented concept? Something more holistic yet sophisticated like design pattern? Or something more brainy like algorithm?

Popular topics interviewer use

Object-oriented concepts

In my previous job, my technical interview is the 1st round of interview after the candidate has passed a codility test. The online test involves assessing candidates basic programming skill (fixing a logical operator in a small function) and writing a basic SQL query with some joins. I think it was necessary to cover the basic of object-oriented concept for a C#.NET developer. So I ended up with asking questions like:

  • Explain to me what are method overloading and method overriding?
  • What are the differences between interface and abstract class?

I was under the assumption these questions were alright until one day I have a candidate who answered me so fluently as if he was reading it out from a book – except he didn’t have a book in front of him. This suggests the candidate have rehearsed these answers a thousand times before talking to me.

Well, the reality is at first I thought the candidate was such a bright developer that knows these concept so well. I decided to give him a little more challenging question to see how far he could go. The question was base on what he has explained earlier where an abstract class can contain both method with empty implementation and concrete implementation; while interface can only contain method signature without implementation. Great!

My next question was, if an abstract class can do both methods with empty implementation and concrete implementation, why do we still need interface? I was expecting him to explain something along the line where a child class can only inherit 1 abstract class but multiple interfaces. I would be happy to accept the answer and prepared move on to the next topic even if he just give me a one liner answer. To my surprised he kept quiet and could not provide any explanation.

From there, I realized there are candidates who really put a lot effort in preparing for technical interview like rehearsing answers for those top 50 interview questions from Google result. Ahem… the truth was, I was too lazy to craft any original interview question back then so I ended up using questions from those top 50 interview questions where candidates can easily prepare for. The problem with this was I ended up evaluating how much preparation work a candidate has done rather than how strong his technical capability is. It was a bad idea to use top 50 interview questions.

The top 50 interview questions

When you use those top 50 interview questions, not only you cannot accurately assess the candidate, you will push away those developers who really know their stuff. Remember interview is about viewing each other between the interviewer and the interviewee. Under normal circumstances, a company will put one of their best guys to conduct the interview. If the best guy in the company can only conduct interview base on top 50 interview questions, it will really make me think twice whether I want to join the company when the company offers me a job.

In fact, I encountered this once. I was talking to an interviewer in a MNC who has prepared a long list of technical questions. We covered those questions in approximately 30 minutes instead of his normal 60 minutes. At one point, after he asked question A, I knew he will follow up with question B, so I explained the answer for question B along with the answer in question A. At the end of the interview, his feedback was it was as if I already have the list of question that he was holding. The truth was, I have gone through those questions 5629 times when I was preparing interview questions for my candidates.

Eventually, I did not take up the offer in the MNC. There are many factors that influenced the decision. One of them is knowing the best technical guy in the team could only do what I did 2 years ago, it wasn’t very motivating.

I have stopped using those top 50 interview questions. They are for amatures 🙂

Design pattern

Design pattern seems like a favorite topic for discussion during technical interview in the past few years. This topic got so popular to the point that a recruiter without a computer science background will start asking candidates to explain design patterns. It took me by surprised when two HR looking ladies (they were recruiters) were asking me to explain the design patterns I have worked with. I got a feeling they did not understand 9 out of 10 sentences came out from my mouth because they never ask any follow up question base on what I explained. They probably just wanted to see how clearly I can articulate my ideas.

Design pattern is something you implement it once and it becomes a second nature in your project. Developers do not apply 7 patterns at a go and revisiting them every 3 weeks to evaluate whether they are still appropriate. If they are not, revamp them and apply another 5 new patterns. This simply do not happen for any software with real delivery timeline. Most developers will be working with 1-2 patterns on a daily basis. This will be a breadth and depth issue. The interviewer might be an expert with Adapter and Abstract Factory while the interviewee is an expert in Observer and Singleton. It is not always possible to have an in-depth discussion on all design patterns.

Shouldn’t a good developer know a few more patterns at least on the theoretical level? Yes, I think it’s a valid point. However there will still be a gap between interviewer and interviewee’s level of understanding. For example, the interviewer has been working with Adapter for the last 3 years and the interviewee only read 3 articles on Adapter pattern (or vice versa). The level of discussion between interviewer and interviewee on Adapter pattern is going to be shallow.

The bad news is, some interviewers doesn’t seem to recognize the breadth and depth gap. Some interviewers insist on discussing rigid details on specific design pattern. It will end up being an unpleasant experience for both interviewer and interviewee. Interviewee feeling inferior for not being able to provide an answer; while interviewer feeling not satisfied because he cannot have a meaningful technical discussion with interviewee to assess his technical skill.

The good news is, when design pattern base questions are done right, it gives both the interviewer and interviewee a good discussion to explore areas they both might not have thought of before as an individual.


This is a very safe approach to use during technical interviews because all programmers are expected to have solid logical thinking. Algorithm is all about combining programming techniques and logical thinking to solve specific problem. It is a very suitable approach to assess interviewee’s ability to solve a problem using codes.

Interview questions base on algorithm could be as simple as writing a function to print a few asterisks (*) on the screen, to detect whether the input is an odd or even number, to sorting a series of numbers, to printing a calendar. Usually the company who uses algorithm base questions will have 3 level questions such as easy, medium, hard. If you want to secure a job, you should at least get it right on easy and medium. The hard question is there for the interviewer to identify a grand-master coder over a senior coder.

The ironic part about algorithm base question is a lot of candidates tend to shy away from them.

Example 1:  About 8 years back it was still pretty common to have the candidate to write down the solution on paper. The question was about a simple string manipulation function. Unfortunately, the candidate who appeared to be an experienced developer handed me empty paper and left with an apologetic tone saying this job might not be right for him.

Example 2: One company that I know of is asking the candidate to code a function to detect an integer input whether is an odd or even number and display an appropriate message – using the provided laptop with Visual Studio on it. The answer is surprisingly simple which is to use a modulus (%) and put an If check at the remainder. However this took a candidate who is applying a senior developer position 20 minutes to type a few keystrokes and a few backspaces, type a few keystrokes and a few backspaces.

Example 3: Codility has been an handy tool for conducting programming test online to save everyone’s time. I recently found out a friend who applied for Tech Lead position. He was asked to write a function to work with zero-based index in Codility. To my surprise, he could not understand the question. He did not even attempt to write the solution and closed the browser.

It appears that interviewee feels very stressful when the technical interview involve writing algorithm. In the above examples, the question was not complicated, the answer was not complex. I believe all 3 candidates in the above examples can do reasonably well if they are not in an “technical interview” mode.

In the next article, I will discuss more about how I conduct technical interview instead…