A data structure is essential for designing algorithms and is a fundamental part of all programming languages. It helps in efficient data organisation and modification. 

A data structure is used to represent the relationship between different forms of data. It helps in increasing the efficiency of the applications of various operations, algorithms and functions.

If you are looking to get a job as a data structuring professional, you need to be familiar with data structures and algorithms and how they work. Going through some of the most frequently asked data structure interview questions can help you prepare and improve your chances of success.

Top Data Structure Interview Questions: 

Q. What is a linear data structure? Explain with examples.

A. You can call a data structure linear if every data item and element is arranged sequentially or in a linear order. The elements get stored in a non-hierarchical manner, ensuring that every item has predecessors and successors with the exception of the first and the last in the list. An Array, Queue, Linked List and Stack are all examples of linear data structures. 

Q. What are some data structure applications?

A. Data structures are used for

• Operating systems
• Numerical analysis
• Database management
• Graphics
• Simulations
• Statistical analysis
• AI
• Compiler designing

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

A. The difference between storage structures and file structures lies in the memory area being accessed. A storage structure is a data structure that exists in the computer system’s memory. File structure represents storage structures stored in the auxiliary memory.

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Q. How are 2D Array’s elements stored in memory?

A. The elements are stored in two ways:

• Row Major Order: In this type of order, all the rows of a 2D array get stored in a contiguous manner in memory. The 2D array’s first row is stored completely in memory. This is followed by the second row, then the third and so on till the last row. 
• Column Major Order: In this style of order, every column of a 2D array is stored in the same order in the system’s memory. The first column is saved completely in memory. Then the second row is stored, followed by the third and so on. By the end, the complete array gets recorded in memory. 

Q. What is a linked list data structure?

A. A linked list data structure is a data object sequence in which the elements don’t get stored in adjacent memory locations. Instead, they are linked through points and form a chain. Every element becomes a node or an individual object. Every node comprises two components - a data field and a reference to the next node. In a linked list, an entry point is known as the head. When a list is empty, the head gets recorded as a null reference. The last node makes a reference to null.

A linked list data structure is applied to situations where:

• You are dealing with an undefined number of items or objects on your list.
• You require constant insertions or deletions from the list like real-time computing with time predictability being critical.
• You don’t require random access to elements.
• The algorithm needs a data structure that allows objects to be stored in memory regardless of their physical address.
• You need to enter items into the middle of the list like in priority queues.

Some common implementations are graphs, stacks and queues, dynamic memory allocation, directory of names and arithmetic operation performance of long integers. 

Q. Are linked lists seen as non-linear or linear data structures?
A. A linked list can be both linear and non-linear as a data structure based on the application it is used for. When you use a linked list for access strategies, it is seen as linear. When it is used for data storage, it is seen as non-linear. 

Q. Why is a linked list better than an array? Also, talk about the situations where linked lists or arrays are used.

A. There are several benefits of linked lists over arrays.

1. Insertion and deletion: Insertion or deletion of nodes is a simpler process, which means linked lists have the upper hand. We generally update only addresses present in the next node pointer. Doing the same thing in an array is more costly because the room must be made for every new element while the current elements need to be shifted. 
2. Dynamic data structure: A linked list follows a dynamic data structure. Therefore, you don’t need to provide an initial size since the data grows and shrinks at its runtime through deallocating and allocating memory. That being said, an array has size limitations since all the elements are stored statically in the main system memory. 
3. No memory wastage: A linked list can decrease or increase based on the program’s demands. Memory is also allocated according to the need at hand. Therefore, no memory gets wasted. On the other hand, arrays cause memory wastage.

It is easier to implement a data structure like a queue or stack using linked lists instead of arrays. 

Some instances where linked lists work better than arrays are given below:

• When you know in advance the upper limit of the number of elements.
• When there are several add or remove operations.
• When there is no large number of random access element requests.
• When you need to add items in the middle of your list, like when you implement a priority queue.

Some instances where arrays work better than linked lists are:

• When you need to randomly access or index elements.
• When you want to know the number of elements beforehand in an array to allocate the appropriate amount of memory.
• When you need higher speed as you iterate every element in the given sequence. 
• When you have limitations or restrictions on memory. A filled array uses less memory than a linked list. Every element in an array is the required data, while every node in a linked list needs data along with one or more pointers for other elements in the list. 

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Q. What is a doubly-linked list? Explain with examples.

A. A doubly-linked list is a complex linked list type. In this type of list, one node has two links. One of them connects to the next node in its sequence and the other connects to its previous node. This enables you to traverse in both directions across data elements. 

Some examples of a doubly-linked list are:

• A playlist with buttons for previous and next song navigation.
• Browsers with options to go back or forward from your present page. 
• The Ctrl/Command + Z and Ctrl/Command + Y functions to undo and redo tasks.

Q. How can you reference all elements in a one-dimensional array?

A. You can access all of a one-dimensional array’s elements via an indexed loop. A counter or timer counts down to 0 from the highest array size (n-1). You can use the loop counter as an array subscript and reference all the items in succession.

Clearing any interview is complex. Practising these data structure interview questions can help you succeed in your next interview. For a more holistic learning, enrol in a data structure training program and prepare for your interview with industry experts.

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