tech-interview-handbook

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cheatsheet

Coding interview cheatsheet

Things you should and shouldn't do during the coding interview

Cheatsheet

algorithm

coding

interview

cheatsheet

checklist

This is a straight-to-the-point, distilled list of technical interview Do's and Don'ts, mainly for algorithmic coding interviews. Some of these may apply to only phone screens or whiteboard interviews, but most will apply to both. I revise this list before each of my interviews to remind myself of them and eventually internalized all of them to the point I do not have to rely on it anymore.

Legend

✅ = Do
❌ = Don't
⚠️ = Situational

Before interview

	Things
✅	Prepare pen, paper and earphones/headphones.
✅	Find a quiet environment with good Internet connection.
✅	Ensure webcam and audio are working. There were times I had to restart Chrome to get Hangouts to work again.
✅	Request for the option to interview over Hangouts/Skype instead of a phone call; it is easier to send links or text across.
✅	Decide on and be familiar with a programming language.
✅	Familiarize yourself with the coding environment (CoderPad/CodePen). Set up the coding shortcuts, turn on autocompletion, tab spacing, etc.
✅	Prepare answers to the frequently-asked behavioral questions in an interview.
✅	Prepare some questions to ask at the end of the interview.
✅	Dress comfortably. Usually you do not need to wear smart clothes, casual should be fine. T-shirts and jeans are acceptable at most places.
✅	Stay calm and composed.
⚠️	Turn off the webcam if possible. Most remote interviews will not require video chat and leaving it on only serves as a distraction.

Introduction

	Things
✅	Introduce yourself in a few sentences under a minute or two.
✅	Mention interesting points that are relevant to the role you are applying for.
✅	Sound enthusiastic! Speak with a smile and you will naturally sound more engaging.
❌	Spend too long introducing yourself. The more time you spend talking the less time you have to code.

Upon receiving the question

	Things
✅	Repeat the question back at the interviewer.
✅	Clarify any assumptions you made subconsciously. Many questions are under-specified on purpose. E.g. a tree-like diagram could very well be a graph that allows for cycles and a naive recursive solution would not work.
✅	Clarify input format and range. Ask whether input can be assumed to be well-formed and non-null.
✅	Work through a small example to ensure you understood the question.
✅	Explain a high level approach even if it is a brute force one.
✅	Improve upon the approach and optimize. Reduce duplicated work and cache repeated computations.
✅	Think carefully, then state and explain the time and space complexity of your approaches.
✅	If stuck, think about related problems you have seen before and how they were solved. Check out the tips in this section.
❌	Ignore information given to you. Every piece is important.
❌	Jump into coding straightaway.
❌	Start coding without interviewer's green light.
❌	Appear too unsure about your approach or analysis.

Code out your solution

	Things
✅	Explain what you are coding/typing to the interviewer, what you are trying to achieve.
✅	Practice good coding style. Clear variable names, consistent operator spacing, proper indentation, etc.
✅	Type/write at a reasonable speed. Too slow is no good.
✅	As much as possible, write actual compilable code, not pseudocode.
✅	Write in a modular fashion. Extract out chunks of repeated code into functions.
✅	Ask for permission to use trivial functions without having to implement them; saves you some time.
✅	Use the hints given by the interviewer.
✅	Demonstrate mastery of your chosen programming language.
✅	Demonstrate technical knowledge in data structures and algorithms.
✅	If you are cutting corners in your code, state that out loud to your interviewer and say what you would do in a non-interview setting (no time constraints). E.g., "Under non-interview settings, I would write a regex to parse this string rather than using `split()` which may not cover all cases."
✅	Practice whiteboard space-management skills.
⚠️	Reasonable defensive coding. Check for nulls, empty collections, etc. Can omit if input validity has been clarified with the interviewer.
❌	Remain quiet the whole time while coding.
❌	Spend too much time writing comments.
❌	Use extremely verbose or single-character (unless they're common like `i`, `n`) variable names.
❌	Copy and paste code without checking (e.g. variables need to be renamed).
❌	Interrupt your interviewer when they are talking. Usually if they speak, they are trying to give you hints or steer you in the right direction.
❌	Write too big (takes up too much space) or too small (illegible) if on a whiteboard.

After coding

	Things
✅	Scan through your code for mistakes as if it was your first time seeing code written by someone else.
✅	Check for off-by-one errors.
✅	Come up with test cases. Try extreme test cases - empty sets, single item sets, negative numbers
✅	Step through your code with those test cases.
✅	Look out for places where you can refactor.
✅	Reiterate the time and space complexity of your code.
✅	Explain trade-offs and how the code/approach can be improved if given more time.
❌	Immediately announce that you are done coding. Do the above first!
❌	Argue with the interviewer. They may be wrong but that is very unlikely given that they are familiar with the question.

Wrap up

	Things
✅	Ask questions. More importantly, ask good and engaging questions that are tailored to the company! Pick some questions from this list.
✅	Thank the interviewer.
⚠️	Ask about your interview performance. It can get awkward.
❌	End the interview without asking any questions.

Post interview

	Things
✅	Record the interview questions and answers down as these can be useful for future reference.
⚠️	Send a follow up email to your interviewer(s) thanking them for their time and the opportunity to interview with them.

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