# 50+ Data Structure, Algorithms & Programming Languages Interview Questions for Programmers

There are a lot of computer science graduates and programmers applying for programming, coding, and software development roles at startups like Uber and Netflix; big organizations like Amazon, Microsoft, and Google; and service-based companies like Infosys or Luxsoft, but many of them have no idea of **what kind of programming interview questions to expect** when you’re applying for a job with these companies.

In this article, I’ll share some frequently asked programming interview questions from different interviews for programmers at different levels of experience, **from people who have just graduated from college to programmers with one to two years of experience.**

Coding interviews are comprised mainly of data structure and algorithm-based questions as well as some of the logical questions such as, How do you swap two integers without using a temporary variable?

I think it’s helpful to divide coding interview questions into different topic areas. The topic areas I’ve seen most often in interviews are array, linked list, string, binary tree, as well as questions from algorithms (e.g. string algorithm, sorting algorithms like quicksort or radix sort, and other miscellaneous ones), and that’s what you will find in this article.

**It’s not guaranteed that you will be asked these coding or data structure and algorithmic questions**, but they will give you enough of an idea of the kinds of questions you can expect in a real programming job interview.Once you have gone through these questions, you should feel confident enough to attend any telephonic or face-to-face interviews.

Btw, there is no point in attempting these questions if you don’t have sufficient knowledge of essential Data Structure and Algorithms or you have not touched them from ages.

In that case, you should take a good course like Algorithms and Data Structures Part 1 and 2 By Robert Horvick to refresh your DS and algorithms skills.

**Top 50 Algorithms and Coding Interview Questions**Without any further ado, here is my list of some of the **most frequently asked coding interview questions from programming job interviews:**

**1. Array Coding Interview Questions**An array is the most fundamental data structure, which stores elements at a contiguous memory location. It is also one of the darling topics of interviewers and you will hear a lot of questions about an array in any coding interview, e.g. reversing an array, sorting the array, or searching elements on the array.

The key benefit of an array data structure is that it offers fast O(1) search if you know the index, but adding and removing an element from an array is slow because you cannot change the size of the array once it’s created.

In order to create a shorter or longer array, you need to create a new array and copy all elements from old to new.

The key to solving array-based questions is having a good knowledge of array data structure as well as basic programming constructors such as loop, recursion, and fundamental operators.

Here are some of the popular array-based coding interview questions for your practice:

**How do you find the missing number in a given integer array of 1 to 100? (solution)****How do you find the duplicate number on a given integer array? (solution)****How do you find the largest and smallest number in an unsorted integer array? (solution)****How do you find all pairs of an integer array whose sum is equal to a given number? (solution)****How do you find duplicate numbers in an array if it contains multiple duplicates? (solution)****How are duplicates removed from a given array in Java? (solution)****How is an integer array sorted in place using the quicksort algorithm? (solution)****How do you remove duplicates from an array in place? (solution)****How do you reverse an array in place in Java? (solution)****How are duplicates removed from an array without using any library? (solution)**

These questions will not only help you to develop your problem-solving skills but also improve your knowledge of array data structure.

If you need more advanced questions based upon array then you can see also see The Coding Interview Bootcamp: Algorithms + Data Structures, a boot camp style course on algorithms, especially designed for interview preparation to get a job on technical giants like Google, Microsoft, Apple, Facebook etc.And, if you feel 10 is not enough questions and you need more practice, then you can also check out this list of 30 array questions.

**2. Linked List Programming Interview Questions**A linked list is another common data structure that complements the array data structure. Similar to the array, it is also a linear data structure and stores elements in a linear fashion.

However, unlike the array, it doesn’t store them in contiguous locations; instead, they are scattered everywhere in memory, which is connected to each other using nodes.

A linked list is nothing but a list of nodes where each node contains the value stored and the address of the next node.

Because of this structure, it’s easy to add and remove elements in a linked list, as you just need to change the link instead of creating the array, but the search is difficult and often requires O(n) time to find an element in the singly linked list.

This article provides more information on the difference between an array and linked list data structures.

It also comes in varieties like a singly linked list, which allows you to traverse in one direction (forward or reverse); a doubly linked list, which allows you to traverse in both directions (forward and backward); and finally, the circular linked list, which forms a circle.

In order to solve linked list-based questions, a good knowledge of recursion is important, because a linked list is a recursive data structure.

If you take one node from a linked list, the remaining data structure is still a linked list, and because of that, many linked list problems have simpler recursive solutions than iterative ones.

**Here are some of the most common and popular linked list interview questions and their solutions:**

- How do you find the middle element of a singly linked list in one pass? (solution)
- How do you check if a given linked list contains a cycle? How do you find the starting node of the cycle? (solution)
- How do you reverse a linked list? (solution)
- How do you reverse a singly linked list without recursion? (solution)
- How are duplicate nodes removed in an unsorted linked list? (solution)
- How do you find the length of a singly linked list? (solution)
- How do you find the third node from the end in a singly linked list? (solution)
- How do you find the sum of two linked lists using Stack? (solution)

These questions will help you to develop your problem-solving skills as well as improve your knowledge of the linked list data structure.

If you are having trouble solving these linked list coding questions then I suggest you refresh your data structure and algorithms skill by going through Data Structures and Algorithms: Deep DiveUsing Java course.You can also check out this list of 30 linked list interview questions for more practice questions.

**3. String Coding Interview Questions**

Along with array and linked list data structures, a string is another popular topic on programming job interviews. I have never participated in a coding interview where no string-based questions were asked.

A good thing about the string is that if you know the array, you can solve string-based questions easily because strings are nothing but a character array.

So all the techniques you learn by solving array-based coding questions can be used to solve string programming questions as well.

**Here is my list of frequently asked string coding questions from programming job interviews:**

- How do you print duplicate characters from a string? (solution)
- How do you check if two strings are anagrams of each other? (solution)
- How do you print the first non-repeated character from a string? (solution)
- How can a given string be reversed using recursion? (solution)
- How do you check if a string contains only digits? (solution)
- How are duplicate characters found in a string? (solution)
- How do you count a number of vowels and consonants in a given string? (solution)
- How do you count the occurrence of a given character in a string? (solution)
- How do you find all permutations of a string? (solution)
- How do you reverse words in a given sentence without using any library method? (solution)
- How do you check if two strings are a rotation of each other? (solution)
- How do you check if a given string is a palindrome? (solution)

These questions help improve your knowledge of string as a data structure. If you can solve all these String questions without any help then you are in good shape.

For more advanced questions, I suggest you solve problems given in the Algorithm Design Manual by Steven Skiena, a book with the toughest algorithm questions.

If you need more practice, here is another list of 20 string coding questions.

**4. Binary Tree Coding Interview Questions**

So far, we have looked at only the linear data structure, but all information in the real world cannot be represented in linear fashion, and that’s where tree data structure helps.

Tree data structure is a data structure that allows you to store your data in a hierarchical fashion. Depending on how you store data, there are different types of trees, such as a binary tree, where each node has, at most, two child nodes.a

Along with its close cousin binary search tree, it’s also one of the most popular tree data structures. Therefore, you will find a lot of questions based on them, such as how to traverse them, count nodes, find depth, and check if they are balanced or not.

A key point to solving binary tree questions is a strong knowledge of theory, e.g. what is the size or depth of the binary tree, what is a leaf, and what is a node, as well as an understanding of the popular traversing algorithms, e.g. pre-, post-, and in-order traversal.

Here is a list of popular binary tree-based coding questions from software engineer or developer job interviews:

- How is a binary search tree implemented? (solution)
- How do you perform preorder traversal in a given binary tree? (solution)
- How do you traverse a given binary tree in preorder without recursion? (solution)
- How do you perform an inorder traversal in a given binary tree? (solution)
- How do you print all nodes of a given binary tree using inorder traversal without recursion? (solution)
- How do you implement a postorder traversal algorithm? (solution)
- How do you traverse a binary tree in postorder traversal without recursion? (solution)
- How are all leaves of a binary search tree printed? (solution)
- How do you count a number of leaf nodes in a given binary tree? (solution)
- How do you perform a binary search in a given array? (solution)

If you feel that your understanding of binary tree coding is inadequate and you can’t solve these questions on your own, I suggest you go back and pick a good data structure and algorithm course like From 0 to 1: Data Structures & Algorithms in Java.

If you need some more recommendations, here is my list of useful data structure algorithm books and courses to start with.

**5. Miscellaneous Coding Interview Questions**Apart from data structure-based questions, most of the programming job interviews also ask algorithm, design, bit manipulation, and general logic-based questions, which I’ll describe in this section.

It’s important that you practice these concepts because sometimes they become tricky to solve in the actual interview. Having practiced them before not only makes you familiar with them but also gives you more confidence in explaining the solution to the interviewer.

- How is a bubble sort algorithm implemented? (solution)
- How is an iterative quicksort algorithm implemented? (solution)
- How do you implement an insertion sort algorithm? (solution)
- How is a merge sort algorithm implemented? (solution)
- How do you implement a bucket sort algorithm? (solution)
- How do you implement a counting sort algorithm? (solution)
- How is a radix sort algorithm implemented? (solution)
- How do you swap two numbers without using the third variable? (solution)
- How do you check if two rectangles overlap with each other? (solution)
- How do you design a vending machine? (solution)

If you need more such coding questions you can take help from books like Cracking The Code Interview, by Gayle Laakmann McDowell which presents 189+ Programming questions and solution. A good book to prepare for programming job interviews in a short time.

By the way, the more questions you solve in practice, the better your preparation will be. So, if you think 50 is not enough and you need more, then check out these additional **50 programming questions** for telephone interviews and these books and courses for a more thorough preparation.

**Now You’re Ready for the Coding Interview**

These are some of the most common questions outside of data structure and algorithms that help you to do really well in your interview.

I have also shared a lot of these questions on my blog, so if you are really interested, you can always go there and search for them.

These common coding, data structure, and algorithm questions are the ones you need to know to successfully interview with any company, big or small, for any level of programming job.

If you are looking for a programming or software development job in 2018, you can start your preparation with this list of coding questions.

This list provides good topics to prepare and also helps assess your preparation to find out your areas of strength and weakness.

A good knowledge of data structure and algorithms is important for success in coding interviews and that’s where you should focus most of your attention.

**Closing Notes**Thanks, You made it to the end of the article… Good luck with your programming interview! It’s certainly not going to be easy, but by following this roadmap and guide, you are one step closer to becoming a DevOps engineer.

If you like this article, then please share with your friends and colleague.

The article was originally published here.

Source: HOB

I needed to compose you that bit of word just to thank you very much as before with the lovely opinions you’ve shared in this case. It is so extremely open-handed with you to give openly all most people might have offered for an ebook to make some cash on their own, most notably considering the fact that you could have tried it in the event you wanted. These ideas also worked to become a great way to realize that most people have the same keenness just like my personal own to know the truth a whole lot more in respect of this problem. I believe there are some more enjoyable instances ahead for individuals who scan your site.

Thanks for every one of your work on this web page. My niece take interest in getting into internet research and it’s really obvious why. Most of us hear all about the compelling way you provide reliable tactics by means of your web site and in addition cause contribution from the others on the idea plus our own princess is always becoming educated a lot. Have fun with the remaining portion of the new year. You’re doing a great job.

Thanks for your whole efforts on this web page. My niece really loves working on investigation and it is obvious why. Almost all learn all of the dynamic medium you provide effective tips and tricks via this website and even strongly encourage participation from visitors about this subject matter then our girl is certainly understanding a lot of things. Take pleasure in the rest of the new year. Your conducting a tremendous job.

I’m also commenting to make you understand what a magnificent encounter my child gained reading through the blog. She noticed such a lot of things, most notably what it is like to have a great helping spirit to make the others really easily understand several impossible topics. You truly did more than my desires. I appreciate you for coming up with such warm and helpful, trustworthy, edifying and in addition fun tips on your topic to Tanya.

My wife and i felt really excited that Michael could deal with his basic research from your ideas he received using your web pages. It’s not at all simplistic to just continually be giving away key points that a number of people have been trying to sell. And we all do understand we have got you to appreciate because of that. All of the illustrations you’ve made, the simple website navigation, the friendships your site assist to promote – it’s got all overwhelming, and it’s really assisting our son in addition to the family consider that this matter is cool, and that’s quite important. Thanks for all the pieces!

My husband and i have been so cheerful Ervin could conclude his web research with the precious recommendations he received through the site. It’s not at all simplistic to simply always be giving away secrets which other folks might have been selling. We consider we need the writer to appreciate because of that. Most of the explanations you have made, the straightforward blog navigation, the friendships you aid to create – it is all remarkable, and it’s really leading our son and the family consider that this topic is thrilling, and that’s extremely pressing. Many thanks for everything!

I definitely wanted to construct a quick word so as to say thanks to you for all the nice ways you are writing here. My extensive internet investigation has at the end been recognized with really good tips to talk about with my neighbours. I would assert that we visitors are undoubtedly lucky to dwell in a remarkable network with very many marvellous people with valuable points. I feel rather fortunate to have used your entire web site and look forward to so many more amazing times reading here. Thank you again for a lot of things.

I simply wished to say thanks again. I do not know what I could possibly have implemented without the entire recommendations provided by you over such a situation. It was the distressing dilemma in my position, nevertheless viewing a new skilled technique you managed it took me to leap with delight. I am thankful for this work and thus believe you find out what an amazing job you were carrying out training most people via a web site. I know that you have never met all of us.