Top 15 Data Structures Interview Questions

Introduction

Data structures go through all of the solutions to common problems in detail and inform you of how productive it is to use. This gives you the ability to select the finest option among all problem-solving decisions. So much data is being generated daily, and there are issues like speed in handling this amount of data. For this, DSA offers methods to manage data effectively. In this article, we are going to discuss some data structures Interview Questions. Here we will discuss the most commonly asked questions.

Learning DSA is necessary if you want to succeed in interviews and get hired at a high-paying company. It shows the ability to problem-solving.

Learning Objectives

In this article, we will learn:

• About Data structures, their types, and applications
• Arrays, queues, and stacks and how they are different from each other.
• Different operations with stacks and queues.
• Some questions related to DSA.

This article was published as a part of the Data Science Blogathon.

Data Structures Interview Questions :

Q1. What is a Data Structure?

It is a particular way of storing and organizing data in a program so that it can be used efficiently. The performance of the program is based on how the data is organized. If the data is not stored efficiently, then the performance of that program will be reduced. There are many types, and we must select the DS that should be used in the program based on the problem statement.

Examples: Arrays, Stacks, Queues, Linked Lists,  Trees, and Graphs.

Q2. What are the Applications of Data Structures?

a. Online Ticket Booking:  Booking tickets has become very easy and popular today. Doubly Circular linked lists are used in building an online ticket booking system.

b. Music Players: We have to perform some operations like next and last. For this, stacks, queues, and doubly linked lists are used.

c. Undo -Redo Operation: Stacks are most suited for this. Because stacks follow Last In First Out. So undo will be the last redo operation

d. Forward and Backward Surfing in Chrome: This is the same as Undo-Redo operations. As discussed, stacks are more suitable.

Q3. What are the Types of Data Structures?

Basically, it is divided into two types. They are linear and non-linear.

Linear Data Structure: If the elements are arranged in order, it is called linear. The last element is linked to the current element, and this current element is linked to the next element.

Arrays, stacks, queues, and Linked lists are some examples.

Non-linear Data Structure: If the elements are not arranged in order like the previous element is not linked to the current element, and this current element is not linked to the next element, then this type is called a non-linear. These are connected to each other randomly.

These include trees, graphs, tables, and sets.

Q4. Explain Arrays Data Structure.

Arrays are linear, in which elements are homogeneous. The array is finite, with all homogeneous elements sorted. For example, if you take an array of size 5 and type integer, all 5 elements of the array should be of type integer.

int arr[5] = {2,12,37,23,48}

Arrays are used in cases where we have to store more than one value. For example, storing the names of all the students in a class

Q5. Is it possible to declare an array without specifying its size?

No, it is not possible to declare an array without a size. If we declare an array, it will give a compile error.

Example: Array= new int[] // Compile error.

Still, we can declare an array without giving the size. For this, we have to declare elements of an array.

Example: int Array[] = {1,2,3,4,5}

Q6. What is Array’s default value?

Every new Array is always initialized with the following default value. The default value for byte, short, int, and long is zero (0).

The default value for Boolean is false.

The default value for float and double is 0.0.

The default value of the string is null.

The default value for user-defined is null.

Q7. Explain about Stacks Data Structure.

Stack is a linear data structure that follows the LIFO(last in, first out). All the elements in the stack follow LIFO. The element which is inserted last will be taken out first. One end of the stack is closed, and the other end of the stack is open. The open end is called the top. Stacks can be implemented using arrays or using linked lists.

Some stack applications are Undo-Redo operations, Matching parenthesis, Backtracking, Expression evaluation like postfix and infix, and Memory management.

Q8. Explain Queues Data Structure.

A queue is a linear data structure that follows the FIFO(first in, first out). All the elements in the queue follow FIFO. The element which is inserted first will be taken out first. Both sides of the queue are open; the open front end of the queue is called the front, and the open back end of the queue is called the rear. All the elements are inserted from the rear end and removed from the front end.

Some queue applications are Breadth-first search algorithms implemented using queues, CPU scheduling operations, Queue in music playlists, and customer service centers.

Q9. What are the Operations done with the Stack?

Operations that are available with stacks are,

Push: Push operation is used to add an element to the stack. The stack now includes this new element at the top.

Pop: The pop operation can remove an element from the stack. The top element is removed.

Top: This top operation returns the top element, which means the first element of the stack.

isEmpty: isEmpty is a boolean-type function that returns true if the stack is empty and returns false if there are elements in the stack.

Size: Returns the size of the stack.

Q10. Write a program to Implement a Stack.

#include <stdio.h>
#include <stdlib.h>
#define SIZE 5

int top = -1, my_array[SIZE];
int i;
void push();
void pop();
void display();

int main()
{
    int choice;
    while (1)
    { 
        printf("\n1.Push the element\n2.Pop the element\n3.Display\n4.End");
        printf("\n\nEnter the choice: ");
        scanf("%d", &choice);

        switch (choice)
        {
        case 1:
            push();
            break;
        case 2:
            pop();
            break;
        case 3:
            display();
            break;
        case 4:
            exit(0);

        default:
            printf("\nInvalid choice!!!");
        }
    }
}

void push()
{
    int x;

    if (top == SIZE - 1)
    {
        printf("\nOverflow!");
    }
    else
    {
        printf("\nEnter the element to add: ");
        scanf("%d", &x);
        top = top + 1;
        my_array[top] = x;
    }
}

void pop()
{
    if (top == -1)
    {
        printf("\nUnderflow!!");
    }
    else
    {
        printf("\nPopped element: %d", my_array[top]);
        top = top - 1;
    }
}

void display())
{
    if (top == -1)
    {
        printf("\nUnderflow!!");
    }
    else
    {
        printf("\nElements in the stack: \n");
        for (i = top; i >= 0; --i)
            printf("%d\n", my_array[i]);
    }
}

Q11. Which Data Structure does Recursion use?

Due to its last-in-first-out nature, stacks are used in recursion. The operating system maintains the stack to save the iteration variables at each function call. When a function is called from the main(), memory is allocated to it.

Q12. Explain Postfix Expression and how you Evaluate it.

An expression with a postfix is one in which the operator comes after the operands. Stack is used for evaluating postfix expression. The Steps to evaluate are as follows:

1. From left to right, read all the symbols

2. Put it in the stack if it is an operand.

3. If it is an operator, pop out two operands, perform the operation, and push the result back into the stack.

4. At last, perform the pop operation to get the result.

Q13. Explain the Operations done with the Queue.

Operations that are available with the queue are,

Enqueue: An element is added to the queue using the enqueue operation at the rear end.

Dequeue: Dequeue operation is used to remove an element from the queue. Element present at the front of the queue is removed.

isEmpty: isEmpty is a boolean-type function that returns true if the queue is empty and returns false if there are elements in the queue.

Front: This front operation returns the front element of the queue.

Rear: This returns the rear element of the queue.

size: Returns the size of the queue.

Q14. What are the Different Types of Arrays?

Basically, there are three types of arrays.

1. One-dimensional arrays

2. Two-dimensional arrays

3. Three-dimensional arrays

One-dimensional arrays: One-dimensional array has contiguous memory locations, elements are stored continuously, and the array has only one index value.

Two-dimensional arrays: Two-dimensional arrays are like tabular arrays. It is like a matrix with rows and columns; in them, it stores data. These two-dimensional array elements are accessed using two indices.

Three-dimensional arrays: Three-dimensional arrays include depth along with rows and columns. It is like a cube that has rows, columns, and depth. Three indices access these elements: the first indicates depth, the second indicates the row, and the third indicates the column.

Q15. What is the Difference between Stack and Queue?

In the stack, the element is added from the front end and removed from the front itself. Whereas in the queue, the element is added from the rear, and the element is removed from the same. Stack follows LIFO( last in, first out), but Queue follows FIFO( first in, first out).

In the stack, insertion is called a push, and deletion is called pop, but in the queue, insertion is called enqueue, and deletion is called dequeue. In a stack, there is only one pointer, and that is top. But in the queue, there are two pointers. They are front and rear.

Conclusion

In this article, we have covered a set of data structures interview questions, focusing specifically on arrays, stacks, and queues, which are fundamental components of data structures. These questions are frequently encountered in interviews, emphasizing the importance of a solid understanding of Data Structures and Algorithms (DSA). Recruiters typically anticipate candidates to possess a basic knowledge of DSA, making it a crucial aspect of interview preparation. Mastering these concepts not only enhances your problem-solving skills but also increases your chances of securing a job.

The key objectives of this article are as follows:

• Thanks to data structures, users find it simple to use the data they need correctly.
• For the creation of effective algorithms, data structures are required.
• Programmers can reduce the time spent using the right data structures when conducting operations.
• Efficiency, reuse, and abstraction are all improved by data structures.

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Amrutha

This is Amrutha, I am pursuing B.Tech in the Computer science Department. I am interested in developing ML Models with python and Data Analysis. And also I have an interest in Web Development. I hope my articles in Analytics Vidhya help you to learn better. Thank you!!