Top Data Structure Interview Questions and Answers

words Alexa Wang

Data structures are an important aspect of computer algorithms. Data structures refer to s method of collecting, storing, and organizing data in a way that it can be accessed easily for various purposes thereafter. Using data structures, coders build code for efficient data management and analytics.

However, it is essential to first know the different types of data structures that exist, as this will be important to determine the way in which information can be retrieved and processed that will be used to build high-performance computer algorithms or programs. In other words, different computer functions perform differently using different data structures.

Thus, the key to efficient programming is in the selection of the right data structure to apply a program or algorithm. Data structures are important in programming for several reasons. To begin with, they provide a systematic organization and a structured way of building and organizing a codebase for efficient programming. Next, data structures simplify complex algorithms when running an application. Further, they optimize memory use during the running of an application. Finally, they make it easy and fast for programmers to discover and fix bugs in a codebase.

Top data structure interview questions and answers

Some examples of data structures are linked lists, arrays, queues, and stacks, as we shall see in the frequent data structure interview questions and answers that we have compiled below. Data structures are used in just about every computer-powered function, including database management systems, computer operating systems, artificial intelligence, statistical analysis, numerical analysis, and image processing among others.

Here are frequent data structure questions you will most likely be asked in an interview.

1. What is the difference between a file structure and a storage structure?

The core difference between the two structures is that in the storage structure, data is stored in the main memory of the computer system, while in the file structure, data is stored in auxiliary memory.

2. Describe the main classifications of data structures and provide examples for each

Data structures are classified into two main categories:

1. Linear data structure. A data structure in which all elements are stored in sequential order. Each succeeding element in the linear data structure is connected to the previous element. Examples of linear data structures are arrays, linked lists, stacks, and queues.
2. Non-linear data structure. A data structure in which elements are not organized in a linear or sequential order. For this reason, an element can be connected to two or more items in the structure. Examples of non-linear data structures include trees, tables, graphs, and sets.
3. Which data structure is the most efficient for a recursion?

A stack commonly referred to as a push-down stack data structure is the most ideal for performing a recursion. The stack data structure is linear in nature, whose operations follow the LIFO (Last in, first out) or FIFO (First in, last out) principle. The addition of elements or removal of existing ones from the stack happens at the top end, where the elements added last would be the first to be removed by virtue of being at the top end of the stack.

4. List the operations found in a stack data structure

Below are some common operations in a stack.

• push operation adds an element at the top of the stack. If the stack is full, the operation returns an overflow condition.
• pop operation removes an element from the stack. Only the top element of the stack can be removed.
• Peek operation lets the programmer see the element that is at the top of the stack. No modification takes place in this operation.
• top operation checks the item at the top of the stack.
• isEmpty operation lets the programmer check whether a stack is empty and prevents the execution of operations. The execution returns a true condition if the stack is empty and a false if not empty.
• size operation lets the programmer check the size of the stack.

5. Explain an array

An array is a linear data structure that collects similar types of data types that are stored in contiguous memory locations. This is the most basic type of data structure from which information can be accessed by using the array index number.

The three types of arrays are

• Indexed arrays in which data elements are stored in a series and are represented by indexes in numerical order, with the first index being the number zero.
• multidimensional arrays represent arrays with more than two dimensions. For example, a two-dimensional array is a table or matrix with rows and columns, while a three-dimensional array is a grid with rows, columns, and depth.
• Associative arrays store key-value pairs and use strings as indexes.

6. What is a linked list data structure?  Explain different types of linked lists

After an array, the linked list is the second most used type of data structure. A linked list comprises data objects known as nodes linked together using a link. Each node is made up of two components, the data field and the link field.

Different types of linked lists are 

• Singly Linked List stores data and the link to the next node. 
• Doubly linked list includes the data, a link to the previous node, and a link to the next node. This allows for two-way access to the data.
• Circular linked list, just as the name suggests, each node links to the next, with the first one linking to the last in a circular direction. 
• Doubly circular linked list has each of its nodes pointing to the next and the previous node. Its last node points back to the first node, and that of the first node has a link pointing back to the last node.
• Header linked list has a header node at the beginning of the list.

7. Are linked lists a type of linear or non-linear data structure?

Linked lists can be classified as linear or non-linear data structures. It is non-linear based on storage and linear based on data access strategy.

8. What is a priority queue, and what is the number of queues that can be used to implement the priority queue? 

A priority queue is a special queue in which each element is allocated a priority value. Elements will be served based on their priority in the queue. A priority queue requires two queues to be implemented. One queue is used for storing actual data, while the other is used for storing priority data.

9. What is a tree data structure? List different types of tree data structures

A tree is a non-linear data structure consisting of data nodes that are connected by edges. Non-linear data structures like the tree store data in a hierarchical format. One node becomes the root of the tree as the other nodes form the children of the root or child nodes. Apart from the root node, any node that precedes another is known as the parent node.

Depending on the number of child nodes, trees are classified as

• General Tree is a tree with no limits set on its hierarchy. Each node can have zero to an infinite (n) number of children.
• Binary tree nodes can have up to two child nodes, i.e., 0, 1, or 2.
• Binary Search Tree is an extension of a binary tree with a number of optional restrictions. The value of the left child node of the Binary Search Tree should be less or equal to that of the parent, while the value of the right child node should be greater than or equal to that of the parent.

10. Name the data structures used in implementing graphs

Graphs can be implemented using three data structures:

• Adjacent matrix
• Adjacency list
• Adjacency set

Conclusion

This is a compilation of the frequent data structure interview questions. The questions asked in an interview will be determined by your experience level and the role that you are being interviewed for. Nevertheless, as a programmer, you need to have prepared adequately by taking a data structure course and learning to gain practical knowledge.