**What is Data Structures and Algorithm?**

Data structure and algorithms are two closely related concepts in computer science. A data structure is a way of organizing and storing data in a computer so that it can be accessed and modified efficiently. Examples of common data structures include arrays, linked lists, stacks, queues, and trees.

An algorithm is a step-by-step procedure for solving a problem or accomplishing a task. In computer science, algorithms are typically used to perform operations on data structures, such as searching for a particular piece of data, sorting a collection of data, or inserting or deleting data from a data structure.

Together, data structures and algorithms form the foundation of computer science, and they are essential for the design and implementation of efficient software systems. The study of data structures and algorithms involves the development of mathematical models to describe and analyze the performance of different approaches to solving computational problems, as well as the implementation of those approaches in programming languages.

**What is the necessity of using Data structures and Algorithms?**

Data structures and algorithms are essential for the design and implementation of efficient software systems. The need for data structures and algorithms arises from the fact that computers have limited memory and processing power, and therefore it is necessary to carefully organize and manipulate data in order to use these resources efficiently.

Data structures provide a way of organizing and storing data in a computer so that it can be accessed and modified efficiently. Different data structures are suited to different types of applications, and choosing an appropriate data structure can have a significant impact on the performance and efficiency of a program.

Algorithms are step-by-step procedures for solving a problem or accomplishing a task. In computer science, algorithms are typically used to perform operations on data structures, such as searching for a particular piece of data, sorting a collection of data, or inserting or deleting data from a data structure.

Together, data structures and algorithms form the foundation of computer science, and they are essential for the design and implementation of efficient software systems. By carefully choosing the right data structure and algorithm for a given problem, it is possible to significantly improve the performance and efficiency of a program.

Here are some important Interview questions on DSA:

**What is the difference between a Stack and a Queue?**

**Stack**: A stack is a linear data structure in which elements can be inserted and deleted only from one side of the list, called the top. A stack follows the LIFO (Last In First Out) principle, i.e., the element inserted at the last is the first element to come out.

**What is the difference between a Stack and a Queue?**

Queue: A queue is a linear data structure in which elements can be inserted only from one side of the list called rear, and the elements can be deleted only from the other side called the front. The queue data structure follows the FIFO (First In First Out) principle, i.e. the element inserted at first in the list, is the first element to be removed from the list.

**What is a Doubly Linked List?**

**Ans: **A Doubly Linked List (DLL) contains an extra pointer, typically called previous pointer, together with next pointer and data which are there in singly linked list.

**What is the difference between a Clustered index and non-clustered index?**

**Ans:** A clustered index is a special type of index that reorders the way records in the table are physically stored whereas a non clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on disk.

**Which data structures are used for BFS and DFS of a graph?**
**Ans: **

Queue is used for BFS (Breadth first search)

Stack is used for DFS (Depth first search).

DFS can also be implemented using recursion.