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## Top 20 Data structures Interview Questions

##### Q1) Explain what is data structure?

The data structure is nothing but an entity where the data is perfectly aligned and it can be manipulated as per the requirement. When we deal with data structure it is not just about one table of data but it is about different data sets and how well they are aligned with each other. Overall, it helps the data to be organized.

##### Q2) Explain what is a linked list?

A linked list is nothing but a sequence of nodes. With this sequence, each node is connected to the following node. It forms a chain of data storage.

##### Q3) Explain the process of how do you reference all the elements in the one-dimension array in detail?

To reference all the elements in the one-dimension array, we have to use an indexed loop. With the help of this, it executes from “0” to array size minus one. By following this process the loop counter will be able to refer all the elements.

##### Q4) List out the areas where the data structure is applied?

The data structure is a vital aspect while handling data. The following are specific areas where the data structure is applied:

1. Numerical analysis

2. Operating systems

3. A.I.

4. Database management

5. Statistical analysis

The above are few areas where the data structure is applied and not limited to.

##### Q5) Explain the terminology LIFO?

LIFO stands for **Last in First Out**.

This process describes how the data is accessed, stored and then retrieved. So the latest data that is stored in the database can be extracted first.

##### Q6) Explain what is a binary tree?

It is one type of a data structure which has two nodes, they have left node and right node.

In a programming language, binary trees are considered to be an extension to the linked list.

##### Q7) Define what is stack?

The stack is considered as a data structure where the top layer element can be accessed. The data is stored in the stack and every time when data is stored, it pushes the data downwards which enables the users to access the latest data from the top layers.

##### Q8) Explain what is multidimensional arrays?

Multidimensional arrays use multiple indexes in order to store data into the database. In a few scenarios, data cannot be stored using a single dimension index, in this scenarios multidimensional arrays are useful.

##### Q9) Explain whether a linked list is considered as a linear or non-linear data structure?

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This is purely determined on the requirement basis, a linked list can be considered as a linear data structure or a non-linear data structure. For example: If the linked list is used on storages, then the linked list is considered as a nonlinear data structure.

If linked lists are used against access strategies then they are considered as a linear data structure.

##### Q10) Explain how does dynamic memory allocation will help you in managing data?

A dynamic memory allocation will help you effectively manage your data by allocating structured blocks to have composite structures which can be flexible, i.e. it can expand and can contract based on the need.

Also, they are capable of storing simple structured data types.

##### Q11) What is FIFO?

FIFO in data terminology it stands as “**First in, First Out**”.

This process defines or depicts how the data is stored inserted and accessed in a queue. Within this process, the data that is inserted at the beginning of the queue will only be extracted or accessed first.

##### Q12) Explain what is merge sort and how it is useful?

A merge sort is nothing but a process where the data is divided and sorted to reach the end goal. Within this process, the adjacent elements are merged and sorted to create bigger elements. These sorted elements are gathered again and made the even bigger list. This process is continuous and repetitive until and unless they have nailed it down to a single sorted list.

##### Q13) List out all the advantages of a linked list?

The important aspect or advantage of a linked list is that it is the perfect data structure where the data can be modified very easily. Also, it doesn’t matter how many elements are available on the linked list.

###### Q14) Explain the main difference between PUSH and a POP?

The two main activities, i.e. Pushing and Popping applies the way how data is stored and retrieved in an entity. So if you check in detail, a Push is nothing but a process where data is added to the stack. On the contrary, a Pop is an activity where data is retrieved from the stack. When we discuss the data retrieval it only considers the topmost available data.

###### Q15) Can you explain with an example how does a variable declaration activity will consume or affect the memory allocation?

The amount of space or memory is occupied or allocated depends upon the data type of the variables that are declared. So let’s explain the same by considering an example: Let’s say the variable is declared as an integer type then 32 bits of memory storage is allocated for that particular variable.

So based on the data type of the variable, the memory space will be allocated.

###### Q16) Define the advantages and disadvantages of the heap compared to a stack?

The advantages of the heap compared to a stack are listed below:

1. Heap is more flexible when compared to a stack

2. Memory space of the heap can actually be allocated and de-allocated as per the need.

On the contrary, disadvantages of the heap compared to a stack is listed below:

1. The memory of the heap is slower when compared to the memory of the stack

###### Q17) Explain how a new data can be inserted in the tree?

The following are the steps that you need to follow to insert the data into the tree:

1. First of all, check whether the data is unique or not ( i.e. check whether the data that you are going to insert doesn’t already exist in the tree).

2. Then check if the tree is empty. If the tree is empty then all you need to do is just insert a new item into the root. If the key is smaller to that of a root’s key then insert that the data into the root’s left subtree or otherwise, insert the data into the right side of the root’s subtree.

###### Q18) Can you tell me the minimum number of nodes that a binary tree can have?

A binary tree is allowed or can have a minimum of zero nodes. Further, a binary tree can also have 1 or 2 nodes.

###### Q19) Explain a little bit about the dynamic data structure?

The nature of the dynamic data structure is different compared to the standard data structures, the word dynamic data structures means that the data structure is flexible in nature. As per the need, the data structure can be expanded and contracted. Thus it helps the users to manipulate the data without worrying too much about the data structure flexibility.

###### Q20) Define what is an array?

While referring to array the data is stored and utilized based on the index and this number actually co-relates to the element number in the data sequence. So thus making it flexible to access data in any order. Within programming language, an array is considered as a variable having a certain number of indexed elements.

###### Q21) Can you tell me the minimum number of queues that are needed to implement a priority queue?

The minimum number of queues that is needed is two. Out of which, one queue is intended for sorting priorities and the other queue is meant for the actual storage of data.

###### Q22) List out all different sorting algorithms that are available and state which sorting algorithm is considered as the fastest?

The list of all sorting algorithms are below:

1. Quicksort

2. Bubble sort

3. Balloon sort

4. Radix sort

5. Merge sort

Out of the above sorting options, none of the sorting algorithms can be tagged as the fastest algorithm, because each of these sorting algorithms is defined for a specific purpose. So based on the data structure and data sets available the sorting algorithms are used.

###### Q21) Explain what is a dequeue?

A dequeue is nothing but a double-ended queue. Within this structure, the elements can be inserted or deleted from both sides.

###### Q22) Explain the process of how a selection sort works?

A selection sort is a process where it picks up the smallest number from the entire data set list and places at the beginning. The same process is continued where the second position is already filled in. The same process is continued all the way until the list is completed. The selection sort is defined as a simple sort algorithm when compared to others.

###### Q23) Explain what is a graph?

A graph is nothing but a type of data structure which has a set of ordered pairs. In turn, these pairs are again acknowledged as edges or arcs. These are used to connect different nodes where the data can be accessed and stored based on the needs.

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