Top 50 Data Structures Interview Questions and Answers: An Overview

In this article, we will explore Data Structure Interview Questions and Answers, Data Structure Interview Questions for Freshers, DSA Interview Questions and Answers for experienced professionals. Additionally, we'll also delve into Data Structure Certification Training and provide a comprehensive Data Structure Tutorial to help you enhance your Data Structure skills.

Data Structure Interview Questions for Freshers

1. What is a Data Structure?

The method that describes how to arrange and work with the data is called a data structure. It describes their relationship as well. Data structures include concepts like arrays, queues, stacks, linked lists, and more.

2. Can you describe the different types of Data Structures?

There are two main types of Data Structures:

1. Linear Data Structure: If every element in a data structure is placed in a sequential order, the structure is referred to as linear. All elements in linear data structures have predecessors and successors, with the exception of the beginning and last elements, which are stored in a non-hierarchical manner.
2. Nonlinear Data Structures: Each item or element in the non-linear data structure is related to two or more other items in a non-linear arrangement; it does not form a sequence. There is no sequential structure to the data elements' arrangement.

   Read More about Types of Data Structures

Watch Now !!What are Data Structures? | Types of Data Structures Explained

3. What are some popular Data Structure applications?

Here are a few real-time data structure applications:

• Decision Making
• Genetics
• Image Processing
• Blockchain
• Numerical and Statistical Analysis
• Compiler Design
• Database Design and many more

4. Describe the distinction between storage and file structures.

The memory area accessed makes a difference. A file structure indicates a storage structure in an auxiliary memory, while a storage structure refers to a data structure in the computer system's memory.

5. Which data structures are often used in hierarchical data models, network data models, and relational database management systems?

• RDBMS makes use of the Array data structure
• The network data model makes use of Graph in the data structure
• The hierarchical data model makes use of Trees in data structure

6. Which type of data structure typically is used when recursion is carried out?

The stack data structure is used in recursion in data structure because it is last in first out. To save the iteration variables at each function call, the operating system keeps the stack maintained.

7. Describe a stack and explain how it operates.

A stack in the data structure is an ordered list where changes can only be made at one end, referred to as the top. The data structure is recursive and contains a pointer to its uppermost element. The Last-In-First-Out (LIFO) list, which denotes that the element added to the stack first will be removed last, is another name for the stack.

8. What are some examples of applications that make use of the stack data structure?

• Prefix, postfix, & infix expression evaluation, expression, or conversion
• Syntax parsing
• Reversing a string
• Parenthesis checking
• Backtracking
• Memory Management
• Calling and returning a function

9. What kinds of operations are possible on a Stack?

There are three basic operations that can executed by stack in data structure:

• PUSH: A new element is inserted into the stack via the push action. The top of the stack is occupied by the new feature.
• POP: The top member of the stack is removed using the pop operation.
• PEEK: A peek action does not remove the top element from the stack; instead, it returns its value.

10. Describe a stack overflow condition and explain how it happens.

When the stack data structure reaches its maximum size (Maxsize) and is unable to hold more components, a data structure's stack overflow condition happens. This usually occurs as a result of:

• Adding more items on the stack than it can hold at once, results in the "top" index reaching Maxsize - 1.
• Failing to remove components from the stack to make space for new ones, causes an overflow when you try to add more.

11. Is it possible to distinguish between a stack's POP and PUSH operations?

The ways in which data is stacked and retrieved are defined by the PUSH and POP procedures.

• PUSH: The data being "inserted" onto the stack is indicated by the PUSH command.
• POP: POP describes how to retrieve data. It denotes the removal of data from the stack.

12. Explain the process of adding and removing an element from a stack.

Push:

• To enable it to refer to the next memory allocation, increase the variable top.
• Copy the item to the top of the array at the array index value.
• Proceed step by step until the stack overflows.

Pop:

• Put the element at the top into a different variable.
• Lower the top element's value.
• Return the element at the top.

13. What is an expression with a postfix?

A postfix expression is one where the operators come after the operands. The primary advantage of this format is that it eliminates the need to take operator precedence into account or group sub-expressions in parenthesis. In postfix notation, the expression "a + b" will be written as "ab+".

14. Give the expression's postfix form: (A + B) * (C - D).

The expression (A + B) * (C - D) has the following postfix form, which is also referred to as Reverse Polish Notation, or RPN: AB+CD-*

15. When evaluating arithmetic expressions utilizing the prefix and postfix forms, which notations are used?

When evaluating arithmetic expressions using prefix and postfix forms, the following notations are often used:

• Prefix Notation (or Polish Notation): Polish notation, often known as prefix notation, arranges the operators before the operands.
• Postfix Notation (or Reverse Polish Notation, RPN): Reverse Polish Notation, or RPN, often known as postfix notation, arranges the operator after the operands.

16. What is an array, and how are elements in a one-dimensional array referenced?

An array in data structure is a grouping of related sorts of data elements kept in contiguous memory regions. It is the most basic data structure, where each data element has an index number that may be used to access it at random. An indexed loop with a counter that runs from 0 to the array size minus one can be used to accomplish this. This way, you may use the loop counter as the array subscript to refer to every element in order.

17. Explain the concept of a Multi-Dimensional Array and how its Components are kept in Memory.

An array of arrays where data is collected and organized into rows and columns is known as a multidimensional array. To develop a data structure that looks like a relational database, 2D arrays are created. It makes it simple to store a large amount of data at once that may be transferred to numerous functions as needed.

18. How can one determine the address of a randomly selected element in a 2D array given its base address?

• Row-Major Order: The address of an element a[i][j] of an array stored in row-major order is determined as follows if the array is specified as a[m][n], where m is the number of rows and n is the number of columns. Address(a[i][j]) = B. A. + (i * n + j) * size
• Column-Major Order: The address of an element in an array stored in column-major order, a[i][j], is determined as follows if the array is declared as a[m][n], where m is the number of rows and n is the number of columns. Address(a[i][j]) = ((j*m)+i)*Size + BA.

19. Describe the Linked List data structure.

A sequence of linked nodes (or items) connected by links (or pathways) can be created as a linked list data structure. The next node in the series is indicated by each link, which represents an entry into the linked list. The order in which nodes are generated dictates the order in which they are added to the list.

20. Are Linked Lists considered linear or non-linear data structures?

Linked lists can be classified as linear or non-linear data structures based on the purpose for which they are utilized. Regarded as a linear data structure, it is used for access techniques. It is regarded as a non-linear data structure when utilized for data storage.

DSA Interview Questions for Intermediates

1. What are the advantages of linked lists over arrays?

• A linked list's size can be increased at runtime, whereas an array's size cannot be changed.
• Nodes can be kept anywhere in the memory that is connected by links; the List does not have to be continuously present in the main memory if contiguous space is not available.
• While the array is statically kept in the main memory and requires size declaration at compile time, the list is dynamically put there and expands based on program demands.
• While the number of elements in an array is limited by the array's size, the number of elements in a linked list is restricted by the amount of RAM that is available.

2. Define a doubly linked list.

The doubly linked list is a more complex linked list in which each node carries a pointer to the previous and next node in the sequence. A node in a doubly linked list comprises three components: node data; the next pointer, which is a pointer to the node after it in the sequence; and the prior pointer, which is a pointer to the node before it.

3. Describe the various kinds of array data structures in detail.

There are numerous types of arrays in data structure, including:

• One-dimensional array: A single index value is used to access the elements of a one-dimensional array, which are kept at consecutive memory regions. All of the components are arranged in a series within this linear data structure.
• Two-dimensional array: A tabular array with rows and columns that holds data is called a two-dimensional array. M rows and N columns are grouped into N rows and columns to generate an M × N two-dimensional array.
• Three-dimensional array: A three-dimensional array is a grid that includes rows, columns, and depth as a third dimension. It consists of a cube with three dimensions: depth, rows, and columns. There are three subscripts in the three-dimensional array for each place in a given row, column, and depth. The first index is depth (a dimension or layer), the second is row, and the third is column.

4. Which pointer type should be used in C when creating a heterogeneous linked list?

Since the heterogeneous linked list contains a variety of data types, standard pointers cannot be used in this situation. The void pointer is a general pointer type that may store a pointer to any type, so you must use it for this purpose.

5. Describe the Queue data structure.

An ordered list or linear data structure with elements accessed via the First In First Out (FIFO) method is specified by an abstract data type called a queue in data structure. Only one end, known as REAR, is available for insert operations, and the other end, known as FRONT, is available for deletion actions.

Watch the Video - Queue in data structure

6. What are some examples of Queue data structure applications?

The queue's applications are listed as follows:

• A common usage for queues is as waiting lists for a single shared resource, such as a CPU, disc, or printer.
• Queues are used for asynchronous data transfers, such as file IO, sockets, and pipes, where data is not sent between processes at the same rate.
• Most applications, including CD players and MP3 media players, use queues as buffers.
• In media players, queues are used to manage the playlist and add and remove music from the playlist.
• Operating systems use queues to manage interrupts.

7. What are the disadvantages of using an array to build a queue?

• Wastage of Memory: Because elements may only be inserted at the front end and the value of the front may be so high that all of the space before that can never be filled, the array space used to store queue elements can never be reused to store the elements of that queue.
• Array Size: Choosing the appropriate array size is a constant challenge when implementing a queue using an array since there may be circumstances in which we need to expand the queue to accommodate additional elements. If we utilize an array to create the queue in the data structure, this will be nearly hard to do.

8. What kinds of situations allow for the insertion of elements into a circular queue?

• If (rear + 1)%maxsize = front, the queue is full. Then overflow happens, making it impossible to perform insertion in the queue.
• If rear != max - 1, the rear is going to be increased to the mod(maxsize) as well as a new value will be inserted at the rear end of the queue.
• If front != 0 and rear = max - 1, it indicates the queue is not full therefore, set the value of rear to 0 as well as insert the new element there.

9. What is a Double-ended Queue, or Dequeue?

A dequeue, sometimes referred to as a double-ended queue in a data structure, is an ordered collection of components in which additions and deletions can be made at either or both of the ends or front and back.

10. What is a queue with a priority?

An abstract data type called a priority queue in a data structure is comparable to a queue in that each element has a priority value. The priority of an element (i.e., the order in which it is deleted) determines the order in which elements in a priority queue are served. The components are served in the order they appear in the queue if they have the same priority.

11. Define the Tree data structure.

A single node is identified as the tree's root, while the remaining nodes are referred to as the root's progeny. The Tree is a recursive data structure comprising one or more data nodes. All nodes that have the root node are divided into nonempty sets, with each node being referred to as a sub-tree.

12. List the many types of trees.

The following lists the six different kinds of trees:

• General Tree
• Forests
• Binary Tree
• Binary Search Tree
• Expression Tree
• Tournament Tree

13. Explain the meaning of binary trees and their uses.

A binary tree in a data structure is used to arrange data so that it may be efficiently retrieved and altered. It is a data structure in which the data is represented by two nodes, referred to as leaves and nodes.

14. What does a data structure's hashmap mean?

With the right key, data can be accessed in constant time (O(1)) complexity using the hashmap data structure, which is an implementation of a hash table data structure.

Watch the Video - HashMap/Hash table In DSA

15. Describe an AVL tree.

A height-balancing binary search tree known as an AVL (Adelson, Velskii, and Landi) tree occurs when the difference between the heights of a node's left and right subtrees is either zero or less than one. This prevents the binary search tree from becoming skewed, therefore controlling its height. When working with a huge data set, this is used to continuously prune the data by adding and removing entries.

DSA Interview Questions for Experienced

1. What functions do AVL trees provide?

On the AVL tree, we are able to do the following two operations:

• Insertion: The procedure for inserting data into an AVL tree in the data structure is the same as that for a binary search tree. It might, however, result in an AVL tree property violation, necessitating the balance of the tree. The tree can be balanced by doing rotations.
• Deletion: Similarly to a binary search tree, deletion can also be carried out in this way. The tree's equilibrium might be upset by deletion, thus several kinds of rotations are used to restore it.

2. What are the advantages of AVL trees over Binary Search trees?

By preventing it from becoming skewed, the AVL tree regulates the height of the binary search tree. In a binary search tree of height h, the total processing time is O(h). But in the worst-case scenario, if the BST skews, it can be stretched to O(n). The AVL tree sets an upper limitation on each operation to be O(log n), where n is the number of nodes, by restricting this height to log n.

3. Explain the meaning of a B-tree data structure.

One kind of m-way tree that is frequently used for disc access is the B Tree. There can only be m-1 keys and m children in a B-Tree with order m. The capacity of a B tree to store a large number of keys in a single node and large key values while maintaining a relatively small tree height is one of the main justifications for its use.

4. Distinguish between B+ and B-trees.

B Tree	B+ Tree
Search keys are not able to be repeatedly stored.	It is possible to have redundant search keys.
Both internal and leaf nodes have the capacity to store data.	Only the leaf nodes have the ability to store data.
Since data can be found on both internal and leaf nodes, searching for certain data takes longer.	Since data is only available on leaf nodes, searches are completed much more quickly.
Internal node deletion is quite difficult and time-consuming.	Since the element will always be eliminated from the leaf nodes, deletion will never be a complicated procedure.
Leaf nodes can't be connected to one another.	To improve the efficiency of search operations, leaf nodes are connected to one another.

5. Provide some of the real-world applications for tree data structures.

Applications for the Tree data structure:

• Arithmetic expression manipulation
• Symbol Table construction
• Syntax analysis
• Mode of hierarchical data

6. Explain the Graph data structure.

A non-linear data structure consisting of nodes and edges is called a graph data structure. In a network, nodes are also referred to as vertices, while edges are the lines or arcs that join any two nodes.

7. Recognise the differences on a graph between circuits, paths, and cycles.

• Path: A path is an unrestricted series of neighboring vertices joined by edges.
• Cycle: A closed path with the beginning and ending vertices being the same is called a cycle. No vertex in the path may be visited more than once.
• Circuit: A closed path in which the initial and final vertices are the same is known as a circuit. You can repeat any vertex.

8. Discuss the data structures that are often used in graph implementation.

The graph implementation makes use of the following data structures:

• Adjacency matrices in data structure are utilized in sequential representation.
• Adjacency lists data structures are used in linked representations.

9. What distinguishes the Depth First Search from the Breadth First Search?

Breadth First Search (BFS)	Depth First Search (DFS)
It is an abbreviation for "Breadth First Search."	It is an abbreviation for "Depth First Search."
The Queue data structure is used by BFS (Breadth First Search) to determine the quickest path.	The Stack data structure is used by DFS (Depth First Search) to determine the shortest path.
BFS is slower than DFS in this regard.	DFS is faster than BFS in this regard.
When the target is near the source, BFS operates more effectively.	When the target is far from the source, DFS operates more effectively.
BFS requires additional RAM.	RAM requirements for DFS are lower.
Nodes that have been visited more than once are eliminated from the queue.	The visited nodes are added to the stack and subsequently removed when there are no more nodes to visit.
In BFS, there is no way to go back.	The DFS algorithm utilizes the idea of backtracking and is recursive.
First In First Out, or FIFO, is the foundation of it.	The Last In First Out (LIFO) concept serves as its foundation.

10. Describe how the Graph data structure is used.

The following are some applications for the graph:

• Circuit networks make use of graphs, in which component wires serve as the graph's edges and points of connection as its vertices.
• Transport networks use graphs, with stations represented as vertices and routes as the graph's edges.
• Maps that depict cities, states, or regions as vertices and adjacency relationships as edges are made using graphs.
• Program flow analysis uses graphs, with calls to procedures or modules represented as edges and procedures or modules as vertices.

11. When is Binary Search appropriate to use?

An already-sorted list can be searched using the Binary Search algorithm in the data structure. The algorithm uses the divide-and-conquer strategy.

12. What are the benefits of Binary Search in comparison to Linear Search?

Because we make fewer comparisons during a binary search than during a linear search, it is more efficient. When using linear search, we can only remove one element from each comparison if we are unable to locate the desired value; but, when using binary search, we can remove half of the set with each comparison. Compared to linear search, which takes O(n) time, binary search takes O(log n) time. This indicates that binary search in the data structure is faster than linear search when there are more elements in the search array.

Watch the Video - Binary Search in DSA & Linear Search in DSA

13. What benefits does Selection Sort offer?

• It is simple to understand and easy to use.
• Little data sets can be utilized using it.
• Comparing it to bubble sort, its efficiency is 60% higher.

Watch the Video - Selection Sort In DSA

14. Do dynamic memory allotments aid in data management?

Runtime basic structured data types are stored via dynamic memory allocation. It can be used to handle data of any size, in any order, by combining independently allocated structured blocks to create composite structures that can grow and shrink as needed.

15. Describe the distinction between VOID and NULL.

• Whereas Void is a data type identifier, Null is a value.
• While void denotes pointers with no initial size, null denotes an empty value for a variable.
• Null denotes nonexistence, while void indicates existence but inapplicability.

Summary

A complete overview of data structure interview questions is given in this article for individuals with various levels of experience. It covers more complex subjects like graphs, trees, and hash maps in addition to basic ideas like arrays, linked lists, queues, and stacks. The purpose of the questions is to evaluate a candidate's knowledge of data structures, their applications, and their capacity to use the right data structures for problem analysis and solution.