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Interview Questions

Job interviews sometimes can be a daunting task. Especially when you're confronted with those problems with algorithms and data structures.

I'm sure you've been through a lot when you were in school. Linked lists, binary trees, directed acyclic graphs, hash maps, greedy algorithm, divide and conquer, dynamic programming, depth-first search, breadth-first search, and all those good stuff. Not to mention space and time complexity analysis.

Even though computer science classes were a pain in the ***, somehow you managed to complete them all and made your friends and family proud of you. You will definitely remember all those all-nighter days with your classmates trying to build a compiler, a file system, and a network router. It was traumatizing. You realized you can push yourself much further than you thought possible.

Even with years of hard work, you probably wouldn't claim yourself as a master of computer science, because you know there is much more to be learned. But at least you had some level of confidence that you understand the fundamentals of computer science.

Soon after you got yourself a job as a software engineer. You started building awesome stuff. Years have passed by, and things got rusty. Even though you were writing code on a daily basis, you weren't always concerned with implementing algorithms and data structures yourself. In many cases, you were working on the top of some libraries and frameworks to get things done.

More years have passed by, and you started thinking about taking a different set of challenges outside your company. You started responding to recruiting messages on LinkedIn that you have been ignoring. Writing a new resume, phone screening, and online coding tests are usual hurdles to jump over.

Then here we go. You made all the way through the final round of your hiring process and you were invited to an on-site interview. You are standing in front of a big whiteboard. Your interviewer is asking you to write some code to merge two lists of sorted integers. It is supposed to be an easy problem, but writing code on a whiteboard without syntax highlighting, without auto-complete, without any assistance from a compiler or an interpreter whatsoever is a completely different experience when compared to writing code with a highly advanced integrated development environment (IDE) that reads your mind to write as much as half of the code on your behalf.

I recently had serveral job interviews with different companies. Some interviews went well, others were a bit more challenging than they are supposed to be. I've got a few offers and one rejection so far. Some are still in progress and one of them is highly likely going to turn out as a rejection.

I was very lucky that one of the companies that I had an interview with gave me detailed feedback. They shared comments from each of the four interviewers, which is very unusual. In essence, they had a positive evaluation of the behavioral interview (communication skills, personality, cultural fit, leadership, etc.) and the system design interview (designing scalable systems at extreme sizes), but they had some doubts about my coding abilities. Regardless of the outcome, I sincerely appreciate that kind of feedback. That's what keeps me moving forward.

It's okay to fail. It's okay to make mistakes. As Dr. Hong said, you can't always win, but you can always learn. I've created this repository in an attempt to learn from mistakes.

This Repository

This repository contains some on-site interview questions that I have encountered throughout the last few years. I'm still working on providing solutions for some of the problems. No particular company name is mentioned, but those questions are general enough that they can be asked in any tech interview.

The solutions are the best recollection of mime, but could be slightly different from what I actually wrote down on a whiteboard during the interview. There is plenty of room for improvement for each solution I provided, but I wanted to show what kind of code I was able to write under a harsh environment (a whiteboard, time constraints, psychological pressures, etc.)


Keep in mind that:

Getting a complete, working solution is important. Pseudo-code is not enough. Interviewers are generally okay with any language of your choice among popular ones (C/C++, Java, Python, etc.) but I'd avoid using bizarre languages like Whitespace, Brainfuck, or 아희. No matter what language you use, practice to get working code with some time limit. Try to get all the boundary conditions right.

You are generally expected to write code on a whiteboard or on a basic text editor without syntax highlighting. You should be able to run the code in your head comfortably. It may be acceptable to write some fuzzy code that partially works then gradually improve by running the code with a compiler or an interpreter in a real work environment. But that is not how things work at a job interview. For this reason, writing code on an actual whiteboard or a piece of paper is the best way to prepare yourself for tech interviews. If you still insist typing code on your favorite editor, at least try to write code at the entirety, improve the code if possible, simulate all possible edge cases, fix any bug you found. When you think all is good, run your code to see if your code really works.

Last but not least, practice working under tight time constraint. Depending on the format of your interview and the level of complexity of the problems, you will be given 10-45 minutes per each problem. It is highly unlikely that you will encounter anything super complicated, but problems can be quite challenging under time constraint.

Time Limits

In many cases, a final round consists of multiple interview sessions. The longest one I have had so far was five sessions long. Each interview session runs for about 50-60 minutes. Generally, you and your interviewer will spend some time introducing yourself, with regards to your current role and your past experience, to the other and vice versa. Your interviewer may ask you some behavioral questions. Most interviewers want to leave a few minutes at the end of the session for you to ask some questions. That leaves about 30-40 minutes at most for the coding part itself.

For each problem description, I wrote down how much time I had for that particular problem.


Feel free to submit your solutions via pull requests. Some rules to follow:

  • Your solution must be contained in a single file.
  • Avoid relying on external libraries and frameworks.
  • File name should be in a format of solution-{your GitHub username}.{ext}. For example, if your GitHub username is johndoe and your solution is written in C++, your filename should be solution-johndoe.cpp


Interview questions from multiple tech companies



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