35 Common Data Structure Interview Questions (Plus Example Answers)

If you are seeking a programming, coding or software development position, you should be prepared to answer data structure and algorithm interview questions. Reviewing common questions can help you prepare a thorough, detailed response to impress the hiring manager. In this article, we review common algorithm and data structure interview questions and provide sample answers to help you prepare for your next interview.

These common questions are framed to gain information about your specific knowledge and skills:

How did you learn to code?

Where did you attend college?

What was your major?

What is your highest level of education?

How long have you worked in programming?

How did your last position prepare you for this role?

Did your last position involve data structures?

Are you comfortable working on a team?

Will you be able to explain data structures to colleagues unfamiliar with programming?

Have you held a leadership role before?

Your answers to these general questions will show the interviewer that you understand how data structures work.

What is a data structure?

What is an array?

What is a multi-dimensional array?

What is a linked-list data structure?

What is a recursive data structure?

What is string coding?

What is a binary tree?

What is a merge sort?

What is the difference between “null” and “void?”

What is the difference between a “push” and a “pop?”

What is data abstraction?

What is a postfix expression?

What is a dequeue?

What is Huffman’s algorithm?

How many queues do you need to execute a priority queue?

Here are common algorithm and data structure interview questions with explanations and example answers.

Your answer will demonstrate your understanding of what the interviewing company does. Show you will be able to appropriately structure their data by referencing elements specific to the company.

“Data structures can effectively be applied anywhere data exists. However, it is most useful in database management, analyzing numbers, graphics and compiler design.”

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

“I can describe two ways in which you can do this. First, you can use an iterator. To do so, you need to create a new ArrayList. Then you need to 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 will automatically remove duplicates as it does not allow the latter. The LinkedHasSet should be converted back to an ArrayList, which will then contain all elements with duplicates removed.”

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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.

“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.”

A linked list is a data structure that, like an array, is linear. However, whereas an array stores its elements in contiguous locations, 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, you should have a solid knowledge of recursion as it is a recursive data structure.

“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.”

Dynamic programming involves separating a complex problem into simpler sub-problems and storing the solution to each sub-problem. That way, a programmer doesn’t need to recompute the solution. Using a Fibonacci sequence can decrease run times in a program. You should be comfortable with algorithms and coding to answer this question since there are many different methods to write this sequence.

“public long fibonacci(int x) {

if (x < 0) return – 1;

if (x == 0) return 0;

long[] cache = new long[x + 1];

for (int i = 1; i < cache.length; i++) {cache[i] = -1;}

cache[1] = 1;

return fibonacci(x, cache);

}

private long fibonacci(int x, long[] cache) {

if (cache[x] > -1) return cache[x];

cache[x] = fibonacci(x – 1, cache) + fibonacci(x – 2, cache);

return cache[x];

}”

The binary tree is a data structure that, unlike arrays and linked lists, does not store elements in a linear fashion, but hierarchically. This binary tree questions test your ability to evaluate or delete an expression. To answer this question, you should be able to visually show how to create a postorder recursion for the hiring manager to see your process.

“A post-order tree traversal of node “n” involves the following steps, starting from the root:

The left subtree of n is traversed by calling printPostorder(n.left).

The right subtree of n is traversed by calling printPostorder(n.right).

Then the node n itself is visited.”

Bit manipulation allows a programmer to work with bits as opposed to the abstractions used in modern programming languages. They normally use this kind of programming to detect and correct algorithms, low-level device control, data compression, optimization and encryption algorithms. Bit manipulation makes use of bitwise operations, which is a level of operation that works with individual bits, which are the smallest units of data. To answer bit manipulation questions, you should be familiar with bitwise operations.

“When two integers have opposite signs, it means that their most significant bits are different. The most significant bit of any negative number will always be one, whereas the most significant bit for positive numbers will always be zero. If you apply the bitwise operator exclusive OR (XOR “^”) to two integers with opposite signs, you will get a negative number. This means that if the XOR operator is applied to two integers and returns less than zero, the two numbers have opposite signs.”

When you attend an interview that could involve programming questions, consider bringing a notepad and a writing utensil so you can offer visual responses. The interview space may have a whiteboard where you can write lines of code, but you should go to the interview prepared with your own writing materials.

Your answer will show the interviewer you understand multiple forms of data structures. It will also demonstrate your ability to problem solve, prioritize and make quick decisions.

“The best data structure to use if you want to move the elements of a connected list around is the linked-list structure. You just change the list rather than creating the array.”

Your answer will demonstrate the ease with which you can discuss common data structure terms. If applicable, add an example of how the differences between an array and a stack might apply to the interviewing company.

“Stacks and arrays store data in two different ways. First, there’s the type of data. Stacks can store different types of data while arrays store data of the same type. Second, there’s the size of the structure. Stacks change in size as elements are removed or added. Arrays do not change in size.”

Your answer should demonstrate your knowledge of basic data structure. It will also show the hiring manager that you can explain programming terms and ideas clearly.

“Linear data structures and hierarchical data structures both describe the relationships between pieces of data, but they differ in how the data interacts. Linear data structures organize data in a single-level sequence. Hierarchical data structures organize data in a multi-level configuration.”