# DS Interview Questions & Answers

Posted On:June 7, 2019, Posted By: Latest Interview Questions, Views: 197, Rating :     ## Best DS Interview Questions and Answers

Dear Readers, Welcome to DS Interview Questions and Answers have been designed specially to get you acquainted with the nature of questions you may encounter during your Job interview for the subject of DS. These DS Questions are very important for campus placement test and job interviews. As per my experience good interviewers hardly plan to ask any particular questions during your Job interview and these model questions are asked in the online technical test and interview of many IT companies.

### 1. Define Data Structures

Data Structures is defined as the way of organizing all data items that consider not only the elements stored but also stores the relationship between the elements. ### 2. Define primary data structures

Primary data structures are the basic data structures that directly operate upon the machine instructions. All the basic constants (integers, floating-point numbers, character constants, string constants) and pointers are considered as primary data structures.

### 3. Define static data structures

A data structure formed when the number of data items are known in advance is referred as static data structure or fixed size data structure.

### 4. List some of the static data structures in C

Some of the static data structures in C are arrays, pointers, structures etc.

### 5. Define dynamic data structures

A data structure formed when the number of data items are not known in advance is known as dynamic data structure or variable size data structure.

### 6. List some of the dynamic data structures in C

Some of the dynamic data structures in C are linked lists, stacks, queues, trees etc.

### 7. Define linear data structures

Linear data structures are data structures having a linear relationship between its adjacent elements. Eg) Linked lists

### 8. Define non-linear data structures

Non-linear data structures are data structures that don’t have a linear relationship between its adjacent elements but have a hierarchical relationship between the elements.

Eg: Trees and Graphs

### 9. Why we need cursor implementation of linked lists?

Many languages such as BASIC and FORTRAN do not support pointers. If linked lists are required and pointers are not available, then an alternative implementation must be used known as cursor implementation.

### 11. List the basic operations carried out in a linked list

The basic operations carried out in a linked list include:

Creation of a list

Insertion of a node

Deletion of a node

Modification of a node

Traversal of the list

It is not necessary to specify the number of elements in a linked list during its declaration

Linked list can grow and shrink in size depending upon the insertion and deletion that occurs in the list

Insertions and deletions at any place in a list can be handled easily and efficiently

A linked list does not waste any memory space

Searching a particular element in a list is difficult and time consuming

A linked list will use more storage space than an array to store the same number of elements

### 14. List out the applications of a linked list

Some of the important applications of linked lists are manipulation of polynomials, sparse matrices, stacks and queues.

### 16. Define a stack

Stack is an ordered collection of elements in which insertions and deletions are restricted to one end. The end from which elements are added and/or removed is referred to as top of the stack. Stacks are also referred as piles, push-down lists and last-in-first-out (LIFO) lists.

### 17. List out the basic operations that can be performed on a stack

The basic operations that can be performed on a stack are

Push operation

Pop operation

Peek operation

Empty check

Fully occupied check

### 18. State the different ways of representing expressions

The different ways of representing expressions are

Infix Notation

Prefix Notation

Postfix Notation

### 19. State the advantages of using infix notations

It is the mathematical way of representing the expression

It is easier to see visually which operation is done from first to last

### 20. State the advantages of using postfix notations

Need not worry about the rules of precedence

Need not worry about the rules for right to left associativity

Need not need parenthesis to override the above rules

### 21. State the rules to be followed during infix to postfix conversions

Fully parenthesize the expression starting from left to right. During parenthesizing, the operators having higher precedence are first parenthesized

Move the operators one by one to their right, such that each operator replaces their corresponding right parenthesis

The part of the expression, which has been converted into postfix is to be treated as single operand

Once the expression is converted into postfix form, remove all parenthesis

### 22. State the rules to be followed during infix to prefix conversions

Fully parenthesize the expression starting from left to right. During parenthesizing, the operators having higher precedence are first parenthesized

Move the operators one by one to their left, such that each operator replaces their corresponding left  parenthesis

The part of the expression, which has been converted into prefix is to be treated as single operand

Once the expression is converted into prefix form, remove all parenthesis

### 23. State the difference between stacks and linked lists

The difference between stacks and linked lists is that insertions and deletions may occur anywhere in a linked list, but only at the top of the stack

### 24. Mention the advantages of representing stacks using linked lists than arrays

It is not necessary to specify the number of elements to be stored in a stack during its declaration, since memory is allocated dynamically at run time when an element is added to the stack

Insertions and deletions can be handled easily and efficiently

Linked list representation of stacks can grow and shrink in size without wasting memory space, depending upon the insertion and deletion that occurs in the list

Multiple stacks can be represented efficiently using a chain for each stack

### 25. Define a queue

Queue is an ordered collection of elements in which insertions are restricted to one end called the rear end and deletions are restricted to other end called the front end. Queues are also referred as First-In-First-Out (FIFO) Lists.

### 26. Define a priority queue

Priority queue is a collection of elements, each containing a key referred as the priority for that element. Elements can be inserted in any order (i.e., of alternating priority), but are arranged in order of their priority value in the queue. The elements are deleted from the queue in the order of their priority (i.e., the elements with the highest priority is deleted first). The elements with the same priority are given equal importance and processed accordingly.

### 27. State the difference between queues and linked lists

The difference between queues and linked lists is that insertions and deletions may occur anywhere in the linked list, but in queues insertions can be made only in the rear end and deletions can be made only in the front end.

### 28. Define a Deque

Deque (Double-Ended Queue) is another form of a queue in which insertions and deletions are made at both the front and rear ends of the queue. There are two variations of a deque, namely, input restricted deque and output restricted deque. The input restricted deque allows insertion at one end (it can be either front or rear) only. The output restricted deque allows deletion at one end (it can be either front or rear) only.

### 29. Why you need a data structure?

A data structure helps you to understand the relationship of one data element with the other and organize it within the memory. Sometimes the organization might be simple and can be very clearly visioned. Eg) List of names of months in a year –Linear Data Structure, List of historical places in the world- Non-Linear Data Structure. A data structure helps you to analyze the data, store it and organize it in a logical and mathematical manner.

### 30. What are the objectives of studying data structures?

To identify and create useful mathematical entities and operations to determine what classes of problems can be solved using these entities and operations

To determine the representation of these abstract entities and to implement the abstract operations on these concrete representation

### 31. What is a Stack? Explain with example?

Definition of Stack

Operations of Stack: PUSH and POP

Example

### 32. Write the algorithm for converting infix expression to postfix expression?

Definition of Expression

Types of expression

Algorithm for infix to postfix expression

Example

### 33. What is a Queue? Explain its operation with example?

Definition of Queue

Operations of Queue: insert and remove

Example

### 34. Explain the applications of stack?

Evaluating arithmetic expression

Balancing the symbols

Function calls

### 35. Write an algorithm for inserting and deleting an element from doubly linked list? Explain linear linked implementation of Stack and Queue?

Operations: insertion and deletion with algorithm

### 36. What are the different binary tree traversal techniques?

Preorder traversal

Inorder traversal

Postorder traversal

Levelorder traversal

### 37. What are the tasks performed while traversing a binary tree?

Visiting a node

Traverse the left sub-tree

Traverse the right sub-tree

### 38. What are the tasks performed during preorder traversal?

Process the root node

Traverse the left sub-tree

Traverse the right sub-tree

### 39. What are the tasks performed during inorder traversal?

Traverse the left sub-tree

Process the root node

Traverse the right sub-tree

### 40. What are the tasks performed during postorder traversal?

Traverse the left sub-tree

Traverse the right sub-tree

Process the root node

### 41. State the merits of linear representation of binary trees.

Storage method is easy and can be easily implemented in arrays

When the location of a parent/child node is known, other one can be determined easily

It requires static memory allocation so it is easily implemented in all programming language

### 42. State the demerit of linear representation of binary trees.

Insertions and deletions in a node take an excessive amount of processing time due to data movement up and down the array.

### 43. State the merit of linked representation of binary trees.

Insertions and deletions in a node involve no data movement except the rearrangement of pointers, hence less processing time.

### 44. State the demerits of linked representation of binary trees.

Given a node structure, it is difficult to determine its parent node

Memory spaces are wasted for storing null pointers for the nodes, which have one or no sub-trees

It requires dynamic memory allocation, which is not possible in some programming language

### 45. Define a binary search tree

A binary search tree is a special binary tree, which is either empty or it should satisfy the following characteristics:

Every node has a value and no two nodes should have the same value i.e) the values in the binary search tree are distinct

The values in any left sub-tree is less than the value of its parent node

The values in any right sub-tree is greater than the value of its parent node

The left and right sub-trees of each node are again binary search trees

### 46. What do you mean by general trees?

General tree is a tree with nodes having any number of children.

### 47. What is the use of threaded binary tree?

In threaded binary tree, the NULL pointers are replaced by some addresses. The left pointer of the node points to its predecessor and the right pointer of the node points to its successor.

### 48. What is an expression tree?

An expression tree is a tree which is build from infix or prefix or postfix expression. Generally, in such a tree, the leaves are operands and other nodes are operators.

### 49. Define right-in threaded tree

Right-in threaded binary tree is defined as one in which threads replace NULL pointers in nodes with empty right sub-trees.

### 50. Define left-in threaded tree

Left-in threaded binary tree is defined as one in which each NULL pointers is altered to contain a thread to that node’s inorder predecessor.

### 51. What is a binary search tree? Explain with example?

Definition of binary search tree

Operations of binary search tree: Insertion and Deletion

Example

### 52. Explain binary tree traversals?

Definition of tree traversal

Types of traversals

Example

### 53. What is a threaded binary tree? Explain its operation with example?

Operations of threaded binary tree: insertion

Example

### 54. Explain the expression trees?

Procedure to construct expression tree

Example

Steps

Example