The most common coding interview questions (and how to answer them)

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A programming interview can be a nerve-wracking affair, but it doesn’t have to be! If you’re preparing for an interview at the company of your dreams, it helps to know the most common programming interview questions and how to answer them. This article has all of that information and more! Check it out to learn everything you need to know about the most common coding interview questions and what to do when you don’t know the answer right away.


There are no stupid questions. In fact, one of your job is to ask a lot of questions. If you can’t think of any, just tell your interviewer that and ask what they would like you to know about their company and position. Do not worry if you don’t know all or even any of these concepts. You are here to learn as much as possible so don’t hesitate to inquire about anything you do not understand. Answering I don’t know is okay and will show humility on your part. But try to make sure it doesn’t happen too often. When in doubt, fake it till you make it. It is perfectly acceptable to say something like I have never used X before but I am familiar with Y and Z which seem similar enough for me to grasp quickly. This shows confidence and experience in your field while still leaving room for growth. And finally, please do not panic! No matter how badly you perform, there is always another opportunity out there waiting for you. The worst thing that could happen is someone saying no to an offer. At least now you know where you stand and can move forward from there. Best of luck to you all!

Picking an algorithm

Often, you’ll be asked to pick an algorithm and implement it in code. If possible, try implementing several different types of algorithms, since there are many ways to solve a problem. Here are some common algorithms that might show up on your next coding interview:
How would you sort a million numbers? Which sorting algorithm would you use? Explain your choice. How would you search for something in an unsorted list of one million numbers? Explain your choice. How would you reverse a string? Explain your choice. How would you find if two linked lists have equal elements? (Note: both lists must be sorted.) Explain your choice. How would you check if a binary tree is balanced? Explain your choice. How would you compute Fibonacci numbers without using recursion or loops? Hint: think about memorization and divide-and-conquer algorithms. What’s another way to say divide and conquer? What are some applications of divide-and-conquer algorithms that aren’t related to computing Fibonacci numbers? Why do we care about divide-and-conquer algorithms, anyway? If I gave you a large data set, how would you store it so that finding specific pieces of information was as fast as possible? Explain your choices. If I gave you a large data set, how would you store it so that reading through it sequentially was as fast as possible? Explain your choices. If I gave you a large data set, how would you store it so that searching through it randomly was as fast as possible? Explain your choices. You’re given a function called merge sort() . It takes in an array of integers and returns another array containing those integers sorted. Describe what happens when you call merge sort() on any array. You’re given a function called merge sort() . It takes in an array of integers and returns another array containing those integers sorted. Describe what happens when you call merge sort() on any array with duplicate values at different indices.

Identifying bottlenecks

Bottlenecks are a feature in our code. They cause unexpected errors and break our applications. One of our primary tasks as programmers is to identify bottlenecks and eliminate them. So how do we know if there’s a bottleneck? One way to detect whether or not there’s a bottleneck is by checking if some parts of our application run slower than others. If so, it’s very likely that we have a bottleneck issue somewhere in our code. The best way to go about identifying these bottlenecks is by testing different scenarios with different types of data. For example, let’s say we want to find out if there’s a bottleneck when processing large amounts of data. In order to test this, we could create two groups: one group with small amounts of data and another group with large amounts of data. We would then compare how long each group takes to process its respective amount of data. If both groups take roughly around the same time to process their respective amounts of data, then we can conclude that there’s no bottleneck present. However, if one group takes much longer than expected to process its data, then we can conclude that there’s a bottleneck present somewhere in our code—most likely due to insufficient memory allocation or inefficient algorithms. This process will help us identify where exactly there’s a bottleneck and what type of data causes it. Once we’ve identified where exactly there’s a bottleneck, we can then try to fix it using various techniques such as refactoring our code or implementing more efficient algorithms.

Testing, testing, testing

If you’re interviewing for a position as a developer, you should expect to be tested on your technical skills. Before you enter an interview room, know what language(s) and tools are being used. Is it C#? Java? Python? Understand which version of each is in use and go into each interview ready to code. See our tutorial How To Ace A Coding Interview: Tips From The Pros for more advice on acing these tests. Remember that if you don’t know something, say so! You have nothing to lose by admitting that there’s something about a question that’s beyond your current abilities. Your interviewer will appreciate your honesty and give you time to do some research before moving forward with other questions. In many cases, they’ll even offer to help point you in the right direction! Don’t get caught up trying to fake knowledge—it can only hurt you in the long run. Rather, find ways to demonstrate that you’re hungry for learning new things and willing to put in effort toward self-improvement. This could mean reading books or blogs about topics outside of your comfort zone or taking free online courses from top universities like Stanford University or Harvard University. There are also countless free tutorials available online from industry leaders like Google at sites like Udacity, Coursera, and EdX. But don’t stop there! Once you’ve got a good grasp on material relevant to a particular job opening, try doing some mock interviews with friends who work in those fields—they’ll be able to tell when you’re giving canned answers versus demonstrating real mastery over a subject matter. And remember, practice makes perfect!

Designing data structures

You’ll also want to practice designing data structures. There are a number of resources available that can help you with this, but one of my favourites is Data Structures and Algorithms Made Easy by Narasimha Karuma chi. This resource breaks down a number of different data structures and guides you through designing your own data structure based on what would be most useful for your situation. It also discusses in-depth strategies on implementing your design. Once you’ve got an understanding of each type of data structure, I recommend practicing writing code in a similar fashion as your internship where you’re asked to solve a problem without any guidance from anyone else. If you get stuck, check out some tutorials online or ask someone who works in programming if they have time to review your work. As long as you show them what you’re working on and explain why it’s giving you trouble, they should be able to point out any mistakes or suggest improvements. If they don’t have time at that moment, ask if there’s another time when they do have time so that way it doesn’t interrupt their workflow too much. Practice makes perfect! Don’t worry about making mistakes because everyone does – even programmers. Your goal here is to learn more about designing data structures and become comfortable talking about your solution while explaining its pros and cons. Be sure to ask lots of questions along the way if you need clarification on anything! The best way to learn something new is by doing it yourself rather than just reading about it in a book. And remember: if you find yourself getting frustrated or running into obstacles, take a break! Programming isn’t meant to be stressful – instead, it’s supposed to be fun!

Java, C++ or Python?

While there’s no right language for you to learn, there are a few that are very popular and in-demand. If you’re looking for a job as a developer or software engineer, it may be worth familiarizing yourself with one of these: C++, Java or Python. You’ll also need skills with object-oriented programming concepts, if you want to work in development. These include classes, objects, inheritance and polymorphism. Most employers will expect at least two years of experience with any given language. The more time you spend practicing your skills, whether on your own or through an organized course, the better off you’ll be when an employer asks about them during an interview. It can also help to get involved with a local meetup group where developers gather to share ideas and learn from each other. They’re often happy to welcome new members who are eager to improve their skills. Even if you don’t live near one, online communities like Stack Overflow offer some of the same benefits. Their forums provide an opportunity to connect with experienced developers who can provide valuable insight into various topics. But just like in real life, remember that it’s always polite to introduce yourself before asking someone for advice—just make sure you do so in writing! And remember not to give up too easily—no matter what question is asked, take some time to research possible answers beforehand and bring them up in conversation during your interview.
There are lots of different ways that companies hire software engineers but by far they all boil down into two categories: phone screens and onsite interviews. Most often, you’ll be asked a series of technical questions over a phone call. It’s important to prepare for these types of interviews so you can demonstrate your knowledge and experience with programming languages, design patterns, object-oriented concepts, databases, security protocols and other similar topics. You may also be asked about your work history or why you want to work for a specific company—so make sure you have answers prepared for those as well! And remember that if it seems like an interviewer is asking something unfair or off-topic, don’t hesitate to ask what exactly they would like you to focus on in your response.

Using regex

Regex is a powerful tool for matching patterns in text, and can be used in many different ways. It’s also a major source of frustration—when regex fails you, it can make you feel as though your world has been brought to an end. Regex is a double-edged sword: You’ll often hear people saying things like never use regex or regex is evil, avoid it at all costs. Both of these sentiments are misleading and inaccurate. If you don’t understand how regex works, then sure, it can be dangerous. But if you understand what regex is doing under the hood and know when to use it appropriately, then there are plenty of legitimate uses for it that will help improve your workflow. For example, I frequently find myself using regular expressions to match email addresses and phone numbers within blocks of text. There are libraries out there that can do some of these things, but they usually involve either loading an external library or passing around string fragments. This means more code for me to write and maintain, which I want to avoid whenever possible. Instead, I prefer writing my own regular expressions whenever possible because they let me focus on solving my problem rather than abstracting away implementation details. When I’m done with my regex, I have one line of code that does exactly what I need it to do. That doesn’t mean every situation calls for regular expressions; sometimes a simple solution is better than a complex one. But when complex is appropriate, understanding how regex works will save you time and effort down the road. So go ahead and start learning about regular expressions now. As long as you understand their limitations, they’re a valuable tool to add to your repertoire.

System design questions

The goal of these questions is to test your ability to implement a system that is maintainable, scalable, and extensible. Your interviewer will likely be looking for details about data structures and algorithms you’ve implemented in languages like Java or C++. Any previous work you’ve done on projects related to your field will probably be relevant here—canvas for specifics during your Q&A with hiring managers during an office visit or phone screen. If possible, try to get some time with other developers who have experience working in similar systems as part of your preparation process. Make sure you have an understanding of data structures and algorithms beyond simple hello world applications before heading into a job interview. Some helpful resources include W3Schools, codeacademy, O’Reilly books, Khan Academy videos/articles, and MIT open courseware classes. Finally: remember that there are no wrong answers! Don’t stress out if you don’t know exactly what your interviewer is talking about; just do your best to understand their question and come up with a solution that works. In addition to being prepared, it can also help to frame your responses around things you’re familiar with. For example, if you worked at a company where they used MongoDB heavily, make sure to mention that when answering questions about NoSQL databases. This helps show off your experience while also giving insight into why certain design decisions were made by your past employer(s). Also keep in mind that sometimes interviewers ask seemingly complex questions because they want candidates to think through solutions themselves. This way, they can see how you solve problems under pressure and gauge your thought process. So even if something seems really complicated, go ahead and give it a shot! There’s no penalty for trying but plenty of reward for getting it right. You might even impress your interviewer with your problem-solving skills.

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