44 Data Structures and Algorithms Interview Questions

If you're preparing for an interview for a software development role, such as a computer programmer, the hiring manager may ask you questions about data structures and algorithms. Knowledge of these concepts is a prerequisite for a software development role as data structures allow computer programs to organise and store data while algorithms help process the data meaningfully. Understanding the questions interviewers can use to test your knowledge of these concepts can help you prepare properly and impress the hiring manager.

In this article, we list different types of data structures and algorithms interview questions, discuss reasons interviewers ask them and provide tips and sample answers to help you articulate convincing responses that demonstrate your knowledge in these aspects of programming.

Please note that none of the companies, institutions or organisations mentioned in this article are affiliated with Indeed.

10 general interview questions

At the beginning of the session, you can expect the hiring manager to ask you general data structures and algorithms interview questions. These questions can help the employer know you personally and determine your ambitions for their role. Examples of these questions include:

1. Tell me about yourself.

2. How did you hear about this job?

3. Why did you become a software developer?

4. What are your plans for the future?

5. What are your goals for this role if employed?

6. What are your strengths and weaknesses?

7. What's your most important software development project to date?

8. What's the biggest disappointment in your career?

9. How do you motivate yourself to complete tasks on time?

10. Do you enjoy working solo or as part of a team?

Related: What Is a Data Engineer? (With Guide on How to Become One)

12 questions about background and experience

As the interview progresses, the interviewer is likely going to shift to questions that help them understand your background and experience. Examples of these questions include:

1. How long have you been in the software development industry?

2. Can you explain the importance of data structures for the effective functioning of computer programs?

3. Tell me about your knowledge of the software development life cycle.

4. What do you know about algorithms? How do they work?

5. What's a data structure?

6. Do you have any certification in data structures and algorithms?

7. What are the applications of data structures?

8. What part of the OSI model do data structures and algorithms occupy?

9. Where did you learn to program?

10. Describe how you're going to explain algorithms to non-technical staff.

11. Do you have any project management experience?

12. Describe how to perform an algorithm analysis.

Related: Backend Developer Path: Steps on How to Become One

15 in-depth questions

In-depth data structures and algorithms questions test your ability to apply your knowledge on the job. These questions are typically technical and can evaluate your response or behaviour in work-related scenarios. Here are examples of these questions:

1. Explain what a stack is and mention three of its functions.

2. Describe three operations you can perform on different data structures.

3. What's the difference between an array and a linked list?

4. What are graphs and how do developers use them?

5. Explain dynamic memory allocation and its importance in the operation of software.

6. What's the difference between storage structure and file structure?

7. What are the two methods for storing 2D arrays in the memory?

8. What are linear and non-linear data structures?

9. Describe how you're going to determine an algorithm's run-time performance.

10. What's your experience with divide-and-conquer algorithms?

11. What's a data tree? List the types.

12. Why is the binary search more efficient than the linear search?

13. Tell me about the major limitations of the bubble sort.

14. What's a tree traversal?

15. When is it appropriate to use either a queue or a hash when implementing LRU cache?

Related: 7 Linked List Interview Questions (With Sample Answers)

7 interview questions with sample answers

Here are some interview questions about data structures and algorithms and sample answers you can use for practice:

1. What's an algorithm, and what are the four types?

This is a general question that a hiring manager can use to test your general knowledge of an algorithm. Your answer can show the interviewer your experience with algorithms and whether you can apply it in their role. A good answer can explain what an algorithm is, its function and the four types.

Example: 'In computer programming, an algorithm is a set of instructions that define the steps required to solve problems or perform tasks. Algorithms are the foundational blocks of operating systems and other computer programs. They're responsible for making decisions on how a software or hardware performs a task or solves a problem. Computer programmers interact with three types of algorithms, including sorting, searching and graph algorithms. Sorting algorithms help sort data in a specific format while searching algorithms, such as linear and binary search, allow users to find a value or record. Developers use graph algorithms to optimise processes'.

Related: Bubble Sorting: Definition, Functions and How It Works

2. What are linear and non-linear data structures used for?

A hiring manager can ask you this question to test your knowledge of the different types of data structures. This is important because data structures have specific applications. A good answer can demonstrate your knowledge of the data structures, their implementation and usage for database tasks.

Example: 'A linear data set is one that forms a linear list or sequence with its elements. Examples of linear data sets include stacks, queues and arrays. A non-linear data structure's traversal of nodes is nonlinear. Graphs and trees are examples of non-linear data structures'.

3. Which sorting algorithm is the fastest?

The speed of an algorithm can have a significant impact on its performance and energy efficiency. Hiring managers can ask this question to know your experience working with algorithms and your familiarity with their characteristics. In your answer, you can mention the fastest algorithm and its applications.

Example: 'QuickSort algorithm is the fastest, thanks to some technical properties. It's cache-efficient, which allows users to maximise the performance of each cache load. It's also easy to adapt to already or mostly sorted inputs. It can also skip some swaps, which is a speed optimisation feature. The algorithm is ideal for scenarios where speed is more important than stability'.

Related: 48 Data Science Interview Questions to Help You Prepare

4. Where can you use data structures?

This question aims to evaluate your knowledge of the application of data structures. Your answer can demonstrate your understanding of what the interviewing company does. Show you're able to appropriately structure their data by referencing elements specific to the company.

Example: 'Data structures can effectively be applied anywhere data exists. However, it's most useful in database management, number analysis, graphics and compiler design'.

5. How are you going to remove duplicates from a given array in Java?

An array is a structure most programming languages use to implement other data structures, such as strings, stacks, queues and lists. Since it's a fundamental data structure, you may encounter several different questions related to arrays during the interview process. To successfully answer this Java array question, have a foundational knowledge of Java and know how to apply constructors, like recursions and loops.

Example: 'I can describe two ways in which you can do this. First, you can use an iterator. To do so, you create a new ArrayList. Then you traverse the original ArrayList, which contains the duplicate values, and store the first appearance of each element in the new ArrayList using the contains() method. The second ArrayList will contain all elements of the original array minus the duplicate elements.

The second, and better, way in which you can remove duplicates from an array, is by creating a LinkedHashSet from the original ArrayList, which automatically removes duplicates as it doesn't allow the latter. Convert the LinkedHasSet back to an ArrayList, which then contains all elements with duplicates removed'.

6. When can you apply a binary search?

The hiring manager might ask a question like this to ascertain your decision-making skills. Answer confidently and provide a real-world example applicable to the hiring company.

Example: 'You can use the binary search algorithm with a list of ordered and sorted elements. The search will start in the middle of the list and then determine from there whether to continue the search at the top end or the bottom end.'

7. How would you detect and remove a loop in a linked list?

The interviewer may ask this question to test your technical knowledge. A linked list is a data structure that, like an array, is linear. An array stores its elements in contiguous locations, whereas linked lists store elements randomly and link them through pointers. Generally, a linked list is a data structure constructed from nodes, each consisting of a data field and a link that points to the next node in the list. Loops in a linked list could cause errors in the program. To answer this question well, have a solid knowledge of recursion, as it's a recursive data structure.

Example: 'To detect and remove a loop in a linked list, you should write a detectAndRemoveLoop function, which checks for loop in a linked list and then removes it if present and then returns true. If no loop is detected, the function returns false'.