Top 6 Important Coding Interview Questions & Answers [For Freshers & Experienced]

Coders are not always the best when communicating their ideas, even though they may be very adept at understanding a coding problem and delivering the best result for it. However, communication is a vital part of the problem-solving process. Hence, coders must learn how to present themselves in interviews and answer questions tactfully. 

Here is a guide to approaching coding interviews, along with the six most crucial coding interview questions and answers. 

Categories of Coding Questions

As coders are an important part of the backend ecosystem, which props up the entirety of the frontend ecosystem, all coders must be aware of the larger system within which they fit. This is why understanding which coding interview questions are important doesn’t just depend on the question itself but rather on an understanding of the types of questions asked. 

Below are the three types of coding questions: 

  • Coding Challenges – These are the kinds of questions any coder must be able to solve. Typically, these questions assess how quickly someone’s mind functions at a given point and how well they can create a fully optimized and self-sustained solution.
  • System Design Understanding – This section of the interview questions will assess whether a coder actively goes beyond their coding silo to understand the larger institution-level tech setup. This is also important for more senior roles – it tells a recruiter that you will be able to fit in the present backend ecosystem without much difficulty.
  • Mathematical and/or General Aptitude – The idea behind these questions is to understand how you make sense of specific questions and think through them. As such, the questions are not coding-specific, but you need to connect the dots across different ways of approaching the same problem.

Let’s look at some questions from the first two types of questions!

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Q 1. Is it possible to convert a single linked list to a double linked list? If yes, how will you do it?

Ans. When a linked list contains elements, each of which has both the previous and the next members and points to all the elements that come before and after, it’s a double linked list. In a single linked list, the elements point to the one after it, not to the one before.

To get a double linked list, make sure your node reads:

private class Node


    Picture data;

    Node pNext;

    Node pPrev;


Another important point: when you are iterating on this node, add a reference to the previous node each time; otherwise, the double link will be lost.

Q.2 Write a simple program to check whether any given number is prime?

Ans. To execute this, we need to first identify the logic that will underpin this bit of code. These will become the conditions you’ll have to check using various commands. So, the conditions we will have to check for are: 

  1. The number cannot be 1 or 0.
  2. If the number is 2, it is prime.
  3. If the number cannot be divided by another number, it is prime.

So the program will read as follows:

    if (n == 0 || n == 1) {

        return false;


    if (n == 2) {

       return true;


   for (int i = 2; i <= n / 2; i++) {

    if (n % i == 0) {

  return false;



    return true;


Q 3. How will you find all the paths for a sum?

Ans. Let’s take a problem involving a number S, for which you are given a binary tree. You must work backward, attempting to calculate the node values of each path gives the number S. The key to providing the correct answer here depends on the understanding that there is not much that you can manually optimize since it’s a run-of-the-mill exhaustive search question. Here, you will have to update the path-sum and use it to call the children recursively. Once this path-sum reaches 0, store it in the result.

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Q 4. Find an equal-sum subset partition.

Ans. The question asks us to find a partition for any given set so that when the individual elements of each sum are added, the result is equal for both the subsets. Now there’s no intuitive way to approach solving this – but there’s an interesting move we can make. We can reduce this complex problem to a simpler one that we already know how to solve.

Basically, we need to suppose that the sum of all elements is S, and S is even – if not, there can be no partition in the first place. With that out of the way, we need to now look for one of the partitions – and if we find this partition, we can narrow down the other through mutual exclusion. With this knowledge, we have effectively transformed the problem into one where we need to find a particular subset within the array with a sum of S/2. Beyond this, the time complexity will be O(NS/2), with N being the array’s overall size.

Q 5. How do you handle deadlines?

Ans. There’s no correct answer to this – you just need to make sure that you prioritize your work and deliver them in due time. For most people looking for roles centered around coding, managing deadlines is an essential part of the overall deliverables. When you answer this question, you need to show that you are aware of its importance at the organizational level. It is crucial to let the interviewers know that you can handle this on a personal scale. If you wish to impress the recruiter, you must also display this skill at a team management level.

So, an example answer could be: “I value deadlines as sacrosanct and make sure I maintain a calendar for all my deadlines. This way, I can deliver on them and remove any possibility of making excuses. I break down large tasks into smaller chunks and deliver on them consistently across the week – this way, I stay motivated and also ensure that the job gets done.”

Q 6. Using quick sort, write a program to sort numbers in place?

Ans. This is a fairly straightforward coding question. The answer to this is written below:

import java.util.Arrays;

public class QuickSortDemo{

    public static void main(String args[]) {

        int[] unsorted = {6, 4, 3, 2, 8, 7, 1, 5};

        System.out.println(“Unsorted array :” + Arrays.toString(unsorted));

        QuickSort algorithm = new QuickSort();


        System.out.println(“Sorted array :” + Arrays.toString(unsorted));



class QuickSort {

    private int input[];

    private int length;

    public void sort(int[] numbers) {

        if (numbers == null || numbers.length == 0) {



        this.input = numbers;

        length = numbers.length;

        quickSort(0, length – 1);


    private void quickSort(int low, int high) {

        int i = low;

        int j = high;

        int pivot = input[low + (high – low) / 2];

        while (i <= j) 

            while (input[i] < pivot) {



            while (input[j] > pivot) {



            if (i <= j) {

                swap(i, j);





        if (low < j) {

            quickSort(low, j);


        if (i < high) {

            quickSort(i, high);



    private void swap(int i, int j) {

        int temp = input[i];

        input[i] = input[j];

        input[j] = temp;




Coding is a vast field including a range of languages, with a massive scope of specialization in each. How much you want to learn of each coding language in context will depend on which role you are looking for in which industry. If you discover that you lack certain hard skills in terms of coding languages, you can always upskill through Upgrad’s MSc in Computer Science. Offered in partnership with Liverpool John Moores University, this course will prepare you for real-world challenges in a variety of business contexts. With flexible financing options and a course schedule that allows you to learn at your pace, you will be the part of upGrad’s community of 40,000+ global learners! 

Also check, upGrad’s Executive PG Program in Software Development is where your hunt ends!

Is it necessary to have soft skills as a coder?

Yes, it is imperative to have soft skills if you are a coder because you will be a part of a bigger ecosystem where you will depend on other people and vice versa. It is essential to communicate your needs and expectations with clarity and to be a team player - both of which are crucial soft skills.

Should I be prepared with personal coding projects?

Yes. It is always helpful to have a portfolio of personal projects to demonstrate what you are capable of doing. If you are a fresher, having a few projects will illustrate your interest and determination.

Which programming languages should I learn?

There’s no one OG programming language that you must learn - all programming languages can be used to achieve something. So, you must understand what goals you wish to accomplish and then choose a language accordingly. Python, for example, is one of the most common programming languages, so learning that will open up a general field. On the other hand, Javascript is a more technical language that will allow you to appear for more specialized roles within the field.

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