How to Crack The Coding Interview With Practicing Only 30 Questions

How to Crack The Coding Interview With Practicing Only 30 Questions As we always suggested in our previous posts, its extremely helpful to practice with coding questions when preparing an interview. Basically you can start with some very general questions from books like Cracking the Coding Interview or Website LeetCode.  And then when it gets close to your interview date, questions from past interviews of your target company will be more helpful. But people may wonder how many questions do I need to prepare? What is the most efficient way to practice with each question?  Obviously memorizing answers to those questions will never work and over the past I saw many people practicing in highly inefficient ways that could only make them feel as if they were improving. Quality is always better than quantity.  If you can take full advantages of each question you prepared, you dont need to practice with hundreds of questions in order to crack the coding interview. In that spirit, Ill give you the most practical tips and hacks now: 1.  Dont check the answer first Itll be totally meaningless if you go directly to the answer without trying to solve the problem first. Most of the time answers look quite natural and straightforward, which gives you the illusion that you could  easily come up with the same  solution. However its not always the case. Without trying to solve the problem by yourself, you wont be able to know whether you are having trouble with this question, which helps you to check knowledge and concepts you are not familiar with. Also by cracking the problem by yourself, youll have the similar experience as an interview, which is exactly what you are trying to practice. 2. Emulate the intense environment as much as possible Lying in your bed with your Facebook/Twitter open, you wont be able to take full advantage of this practice. On the contrary, if you have  done a lot of practice in an environment that is as intense and nervous as a real interview, I wont be surprised when you get your job. The philosophy is extremely simple, just practice with exactly what youre gonna face. To emulate the intense environment as a real interview, here are  some tips: Remove all distractions. Close all unrelated websites, turn off music and your cellphone and find a quiet place as you dont want to be disturbed. If possible, you can also find a meeting room in your current company or a library, which is even better. Set a timer. You wont have 2 hours to solve a simple coding question apparently. Normally within 45min session, youll be asked 1-2 questions depending on the difficulty and 2 questions are more common. So set a timer to have an idea of your speed and Im pretty sure youll realize how slow you are in the beginning. Also with a timer besides, you are very likely to be more nervous. Talk  while thinking. I cant emphasize enough the importance of this point. By keep talking while thinking about the solution, you are actively communicating with the interviewer, which shows both your analysis and communication skills. Also it gives the interviewer a chance to hint  you when he notices that you are not on the right track or get stuck. However its harder than it seems to be and you really need to practice a lot before getting adapt to it. 3. Code the solution   Having a solution in your mind is far from really solving the problem. You wont be able to understand this unless you try to code your solution and youll realize how important it is.  There are several things youd better keep in mind. First of all, dont start coding without a complete  solution in your mind. Many people start writing down their solutions one minute after knowing the question. It seems as if they were faster, but in fact this is the worst thing in an interview. Without a complete solution, its almost for sure that you will get stuck while writing and if somehow you notice that you are not on the right track, youll have to clear everything on the whiteboard and restart. Also some people tend to keep writing meaningless codes when they get stuck, which can only waste their time. Secondly, write on whiteboard or at least paper (I assume you are preparing for an on-site interview, please use some online code sharing tool for phone screen). Again the point is that always practice with whatever youre gonna face in a real interview. If you will be asked to write on whiteboard, theres no point to be proficient in your Emacs text editor. Also many people felt quite uncomfortable the first time they wrote on a whiteboard, so its better to get adapt to it in your daily practice. Lastly, forget about pseudo code. Ive interviewed so many candidates who can elaborate ideas clearly and have put down few lines of pseudo codes to better explain ideas, but eventually failed to write a correct and complete solution, not even close. Once you try to write solid code for every question youve practiced, youll definitely understand how different it is. If you can compile your code as examination, its even better but not necessary I would say. 4. Optimization Its hard to come up with the optimal answer  in the beginning and you should always try to optimize your existing solution in every way. In a real interview, you will be asked to improve your solution with whatever approaches, which is exactly what we are practicing here. In order to optimize your solution, the first thing is always analyze both time and space complexity. In other words, you should analyze the efficiency for every coding question youve practiced. This concept is extremely important in both interviews and real life projects and without a comprehensive understanding of it, you wont be able to optimize your solution and you dont even know how much you can optimize and what to optimize. Sometimes optimization doesnt necessarily mean improving the complexity from O(n^2) to O(n). Even the complexity is still the same, if somehow you can remove some unnecessary calculation, its still better. The last step of this is to compare with the correct answer.  Remember that having a correct solution is not done yet, you need to know the optimal solution. Compare your code with the standard answer and make sure you fully understand the optimal one. 5. Stretch Even for majority of the good candidates, they can at most finish the above four steps. To further take advantage of the interview question, you can ask yourself several follow-up questions to practice. Remember that this approach is not practicing with questions from nowhere, in fact I always ask a lot of follow-up questions if the candidate solved the problem correctly. Whats more, not all follow-up questions I have answers, what I really care is how each candidate analyze the issue step by step rather than the answer he provides. To give you an idea of what kind of follow-up questions you can practice with, here are some great examples: How do you test your solution? Testing is also an important area in interview and you can treat the interview question as a real life project and how can you guarantee the system works as intended? What if the input size is too large to put in memory? How do you refine your solution and analyze the efficiency? What if the input size is too large to put in disk? How do you solve the scalability issue? What if you have infinite amount of memory? Any way to make the solution faster? You can also try to change some restriction of the question, like what if its a normal tree instead of binary tree? What if you can store the dictionary in any data structure you like? Its extremely helpful to think about these follow-up questions and sometimes its also a great practice to come up with good follow-up questions. 6. Compare with other questions As I always emphasized in the previous posts, its important to recognize common patterns in interview questions. Try to think all of the questions youve practiced as a huge network instead of separate dots, in fact there are so many correlations in between and many questions are exactly the same in essence. A good example is for dynamic programming questions, majority of the solutions are of the same pattern (for interview questions). Once you can recognize and summarize this kind of pattern, itll be much easier to think in the right direction. You can check  A Step by Step Guide to Dynamic Programming to know more about this. Try to compare with questions of the same category like trees, linked list, arrays etc. and Im pretty sure youll benefit a lot from this. Conclusion Of course its important to have enough amount of coding questions to practice, but I believe that its more important to prepare smartly. Ive heard so many complaints like Ive finished all the question on website X but I still failed the interview. Again quality is always better than quantity, only when  you are  preparing in an efficient and smart way, can  you really improve your interview skills.