# Top 50 DSA/Data Structure Interview Questions for best preparation

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Do you also want to become a data structure expert, and are involved in interview preparations for this? Or are you a student, who wants to strengthen the concept of your data structure, and want to become better at it?

Whether you are any of these two, today you have visited the right place, where you will be going to know about some such topics related to the data structure, which are usually asked in interviews or any viva.

Here, you will get mostly asked questions in every interview as well as in big companies, which will strengthen your preparation even more. And along with each question, its answer is also given so that the preparation time can be saved.

This article will help you a lot to clear your data structure skills more and get your confidence back and be ready for any job. At the same time, it will also be of great help to those students who want to increase their knowledge in this subject further.

## Data Structure Interview Questions

So let us now know, about similar questions which experts and teachers in this subject ask a lot –

## What is data structure?

A data structure is a method that specifies how to organize and manipulate data. At the same time, it also defines the relationship between them. Some examples of the data structure are – Arrays, Queue, Linked List, Stack, etc. Data structures are a central part of many computer science algorithms, as they enable a programmer to handle data efficiently.

## What are the types of Data Structures?

It is mainly of two types, which are –

### Linear Data Structure

A data structure is linear if all its elements are arranged in sequential order. Also, elements are stored in a non-hierarchical manner, where except for the first and last element, all items have one successor and one predecessor.

### Non-Linear Data Structure

This type of data structure does not form a sequence, that is, each item or element in it is connected to two or more other items in a non-linear arrangement. Also, the data elements are not arranged in a sequential structure.

## What is Stack?

A stack is an ordered list, in which insertion and deletion of data can be done only at one end, which is called the top. It is a recursive data structure, which contains a pointer to its top element. A stack is sometimes also called a last-in-first-out (LIFO) list, meaning that the first element inserted into the stack will be deleted from the end of the stack.

## Which data structure is used to do the recursion?

Due to the “last in first out” (LIFO) nature of the stack data structure, it is used in recursion. Also the operating system maintains a stack to save iteration variables at each function call.

## In which areas the stack data structure is used?

It is used for many types of applications, such as –

• Memory Management
• Expression evaluation
• Function calling and return
• Backtracking

## What operations can be performed on a stack?

Three types of operations can be done in this –

• Push Operations
• Pop Operations
• Peek Operations

## What is the difference between PUSH and POP?

PUSH and POP operations specify how data will be stored and retrieved in a stack.

PUSH – Specifies that the data is being “insert” into the stack.
POP – Specifies that the data is being “deleted” from the stack.

## How is data inserted by PUSH?

Step 1: First increase the variable top in it so that it can refer to the next memory allocation.

Step 2: Then copy the item to the array index value equal to top.

Step 3: Repeat steps 1 and 2 until the stack overflows.

## How is data deleted by POP?

Step 1: Store the topmost element in another variable.

Step 2: Then subtract the value of the top.

## What is postfix expression?

An expression in which the operators obey the operands is known as a Postfix expression. Its main advantage is that it does not have to group sub-expressions in parentheses.

Expression “a + b” will be represented as “ab+” in postfix notation.

## What is an array called?

It is a collection of data items of the same type, which are stored in contiguous memory locations. It is the simplest data structure, in which each data element can be randomly accessed from anywhere by using its index number. The index of the array starts at , and then it goes up one value by one.

## How can all the elements in a one-dimension array be referenced?

This can be done using an indexed loop, such that the counter runs from 0 to array size minus one. And this way, you can reference all the elements in the sequence using the loop counter as an array subscript.

## What is a Multidimensional Array?

A multidimensional array can be defined as an array of arrays, in which data is stored in a tabular form consisting of rows and columns.

2D arrays are relational databases designed to implement a similar-looking data structure.
It provides the ease of holding large amounts of data together, which can be passed to any number of functions as and when required.

## How are the elements of a 2D array stored in memory?

There are two techniques, using which, the elements of a 2D array can be stored in the memory –

### Row-Major Order

In row-major ordering, all the rows of a 2D array are stored contiguously in memory. In this, the first row of the array is completely stored in memory, then the second row of the array is completely stored in memory, and this process continues till the last row.

Address(a[i][j]) = B. A. + (i * n + j) * size

### Column-Major Order

If the array is declared as a [m] [n] where “m” is the number of rows, while “n” is the number of columns, then the address of an element [i] [ The row-major order of the array stored in j] is calculated as follows, then the way to find the address of the element a[i][j] stored in a column-major order array is –

## What is Linked List Data Structure?

A linked list is a collection of randomly stored data objects, which are called “nodes”. In this, each node is connected to its adjacent node through a pointer. It has two fields in one node, a data field that stores data, and a link field, which stores the address of the next node.

## Are linked lists considered linear or non-linear data structures?

• A linked list is considered to be both a linear and non-linear data structure depending on its position.
• Based on the data storage, it is considered a non-linear data structure.
• Same, based on the access strategy, it is considered a linear data structure.

## What are the benefits of using Linked List instead of Array?

The size of a linked list can be increased during runtime, which is impossible in the case of an array.
The data in a linked list does not need to exist continuously in the main memory, and if contiguous places are not available in the memory, the nodes can be stored anywhere in the memory linked via the linked list.
A linked list is stored dynamically in the main memory, and it grows according to the demand of a program, whereas an array is stored statically in the main memory, whose size must be declared at compile time.
The number of elements in a linked list is limited to the available memory space, whereas the number of elements in an array is limited to the size of the array.

## What type of pointer should be used to create a heterogeneous linked list using C language?

Different types of data exist in a heterogeneous linked list; therefore, it is impossible to use normal pointers in it. That’s why for this work, we have to use a generic pointer type such as void pointer because void pointer is capable of storing any type of pointer.

## What is a doubly linked list?

It is a very complex type of linked list, in which a node contains a pointer to its previous as well as to the next node in the sequence. In a doubly-linked list, a node consists of three parts –

• Node’s data
• Address pointer to the next node in the sequence
• A pointer to the previous node

## What is Queue data structure?

A queue can be defined as an ordered list, which at one end enables insert operations, called “REAR”, and the other end enables delete operations, called “FRONT”. is called.

## Explain some uses of Queue data structure?

Some uses of Queue are –

• Queues are widely used as waiting lists for a single shared resource such as printers, disks, CPUs, etc.
• The queue is also used in the asynchronous transfer of data (where data is not being transferred between two processes at the same rate) such as pipe, file IO, socket, etc.
• The queue is used as a buffer in most applications like Mp3 media players, CD players, etc.
• Also, the queue is used to maintain a playlist in the media player to add and remove songs from the playlist.
• The queue itself is also used to handle any kind of interrupts in the operating system. e.t.c.

## What are the disadvantages of Queue’s array implementation?

There are two types of disadvantages to using it, which are –

The space of the Memory Waste -Array, which is used to store the elements of the queue, can never be reused to store the elements of the queue again, as the elements are only placed on the front end. can only be inserted, and the value of the front can be so high that all the space before it can never be filled.

Array Size – There may be situations in which, we may need to expand the size of the queue to insert more elements, and expand the size of an array if we use an array to implement a queue would be nearly impossible. So it is always a problem to decide the correct size of any array.

## What are the scenarios for inserting an element in the circular queue?

If (rear + 1)%maxsize = front, it means the queue is completely full. In that case, overflow occurs, and therefore, insertion cannot be done in the queue.
If rear != max – 1, it will be incremented in the previous mod(max size), and the new value will be inserted into the rear end of the queue.
If front != 0 and rear = max – 1, it means that the queue is not completely full, and therefore a new element can be inserted thereby setting the rare value to 0.

## What is a deque?

A deque, also known as a “double-ended queue”, can be defined as an ordered set of elements in which insertion and deletion can be performed at both ends, i.e. both forward and backward. From the

## What is a tree data structure called?

A tree is a kind of recursive data structure, consisting of a set of one or more data nodes, where one node is designated as the root of the tree, while the rest of the nodes are referred to as the child of the root. Nodes other than the root node are divided into nonempty sets, each of which is to be called a sub-tree.

## How many types of tree data structures are there?

It is of six types –

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

Also, read How to prepare for interview for freshers?

## What are binary trees?

It is a special type of generic tree, in which each node can have a maximum of two child nodes. A binary tree is generally divided into three different subsets – (the root of the node, the left sub-tree, and the right binary sub-tree).

## What will be the maximum number of nodes in a binary tree of height “k”?

The maximum number of nodes in this will be –> 2k+1-1, where k >= 1

## How is an AVL tree more useful than a binary search tree?

The AVL tree controls the height of the binary search tree by not allowing it to be skewed.
The time taken for all the operations in a binary search tree of height “h” is O(h). However, this can be increased to O(n) if the binary search tree becomes significantly skewed in its worst case.
By limiting this height to the “n” log, the AVL tree imposes an upper bound on each operation to be O(log n), where “n” denotes the number of nodes.

## What are the properties of a binary tree?

In the binary tree of the order “m”, “m” has all the properties of that tree, and apart from this many properties are present in it, such as –

• Each node of a B-tree has at most “m” children.
• Every node in a B-tree, except the Root node and the Leaf node, has at least “m/2” children.
• Root nodes must have at least 2 nodes.
• All leaf nodes must be on the same level.

## What are some applications of tree-data structure?

• It is used for syntax analysis.
• Also, it is used for the manipulation of arithmetic expressions.
• It is also used for symbol table construction.
• It is also used in hierarchical data models. e.t.c.

## What is graph data structure?

A graph “G” can be defined as an ordered set G (V, E), where V(G) represents the set of vertices, and E(G) represents the set of edges, Which is used to connect these vertices. A graph can be viewed as a cyclic tree, where the vertices (nodes) maintain a complex relationship, rather than having a parent-child relationship.

## What is the difference between cycle, path, and circuit?

Path – A path is a sequence of adjacent vertices joined at the edges without any restriction.

Cycle – A cycle can be defined as a closed path, where the initial vertex is the same as the final vertex. Also, none of its vertexes can be visited twice.

Circuit – A circuit can also be defined as a closed path, where the initial vertex is the same as the final vertex. But any vertex can be repeated in this.

## Which data structure is used for graph implementation?

For this, the following data structures are used –

In sequential representation, the adjacency matrix is ​​used.

## What are the applications of graph data structure?

The graph has the following applications –

• Graphs are used in circuit networks, where connection points are drawn as vertices, and component wires become the edges of the graph.
• Graphs are also used in transport networks, where stations are drawn as vertices and routes become the edges of the graph.
• Graphs are used in the analysis of program flow, where procedures or modules are treated as vertices, and calls to these procedures are drawn as the edges of the graph.
• Also, graphs are used in maps that draw cities/states/regions as vertices and adjacency relations as edges. e.t.c.

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## Which data structure is used in BFS and DFS algorithms?

In the BFS algorithm, the Queue data structure is used.
In the DFS algorithm, the Stack data structure is used.

## In which scenario, Binary Search is used?

The binary search algorithm is used to search data in the already sorted list. And this algorithm uses the divide and conquers approach method.

## What are the advantages of binary search compared to linear search?

By the way, there are very few things worth comparing in these two searches. However, in an average case, the linear search takes O(n) time to search a list of “n” elements, while the binary search takes O(log n) time to search a list of “n” elements. Is.

## What are the advantages of Selection Sort?

• It is simple and quite easy to implement.
• Also, it can be used for small data sets as well.
• It is 60 percent more efficient than bubble sort. e.t.c.

## What is the difference between NULL and VOID?

• Null is actually a value, while void is a kind of data identifier.
• A null variable only indicates an empty value or space, whereas a void is used to identify pointers to its initial size.

## What are the applications of Multi-Linked Structures?

• It is used in the sparse matrix.
• Also, it is used for index generation as well.

## What is the condition of Stack overflow?

Overflow occurs when top = Maxsize -1.

## Which data structure is used in RDBMS?

RDBMS uses an array data structure.

## Which data structure is used in the network data model?

The Graph is used in the network data model.

## Which data structure is used in the Hierarchical data model?

Use of trees data structure in this data model

Expression: What will be the postfix of (A + B) * (C – D)?
The postfix of its expression is – AB+CD-*

## Which notations are used to evaluate Arithmetic Expressions using prefix and postfix forms?

In these polish and reverse polish notations are used.

## What is the minimum number of queues to be used to implement Priority Queue?

To do this we need two queues. One queue is used to store data elements, and the other is used to store priorities.

## Which type of data structure is used the most in tree construction?

For this, mostly “Queue data structure” is used.

## Wrapping Up

So, hopefully friends you have gained a lot of knowledge with our article on data structure interview questions. If you liked the article share it with your friends so that they can also excel in the data structure and algorithm.