UST Full Stack Developer Interview Questions and Answers

Two coding question and some aptitude

Q1. Oops concepts and basic coding programs
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There are 4 coding questions in first round

Q1. Some basic statistics questions and data structure questions
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Coding related questions. They may ask System design also for experienced developer role.

Q1. Prepare System design interview questions.
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Q2. How security or authentication is implemented in your project.
Ans. 
Security and authentication are implemented using JWT tokens and role-based access control.
• JWT tokens are generated upon successful login and sent in the Authorization header of each request

• Role-based access control is used to restrict access to certain endpoints based on user roles

• Sensitive data is encrypted before storing in the database

• Two-factor authentication is implemented for additional security
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Q3. Tell me about OAuth authenticaion.
Ans. 
OAuth authentication is a protocol that allows secure authorization of third-party applications to access user data without sharing credentials.
• OAuth stands for Open Authorization

• It allows users to grant access to their resources stored on one site to another site without sharing their credentials

• OAuth uses tokens instead of passwords for secure access

• OAuth 2.0 is the current version and is widely used for authenticati...read more
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Q4. React related question also they asked.
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Q1. Basics Javascript
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Q1. Questions on OOPS mainly inheritance Questions on Core Java Tricky questions on collections Questions on Java 8
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Q2. Questions on JavaScript What is a closure
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Round duration - 90 Minutes
Round difficulty - Medium

It was at 9 am in the morning

Q1. 
Add Two Numbers as Linked Lists
You are given two singly linked lists, where each list represents a positive number without any leading zeros.
Your task is to add these two numbers and return the sum as ...read more
Ans. Naive Method
We will use the naive method to add two linked lists. While adding two numbers, we always add digits in the right to left manner. So first, we will reverse both linked lists so that we can easily process the number in this manner.
 
We will be storing the result of the addition in a different linked list. We will start adding the nodes of both linked lists and use another variable ‘carry’ to keep track o...read more
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Q2. 
Cycle Detection in Undirected Graph Problem Statement
You are provided with an undirected graph containing 'N' vertices and 'M' edges. The vertices are numbered from 1 to 'N'. Your objective is to determi...read more
Ans. DFS Approach (Slow)
There is a cycle in the graph only if there is a back edge (back edge is an edge that connects a vertex to another vertex that is discovered before it's parent) present in the graph. To detect a back edge, we will keep track of vertices that have been already visited. If we reach a vertex that is already visited and is not the parent vertex of the current vertex, then there is a cycle in the graph.&n...read more
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Round duration - 50 Minutes
Round difficulty - Hard

Q1. 
Maximum Subarray Sum Problem Statement
Given an array ARR consisting of N integers, your goal is to determine the maximum possible sum of a non-empty contiguous subarray within this array.
Example of Sub...read more
Ans. Brute Force
We will iterate through all possible boundaries of the subarrays in the given array with the help of two nested loops. 
 
Then, we will iterate through each subarray with the help of another loop and find the sum of the subarray. We will maintain the maximum subarray sum through our iterations and finally return it.
Space Complexity: O(1)Explanation:
O(1), constant space is used.
Time Complexity: O(n^3...read more
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Round duration - 30 Minutes
Round difficulty - Hard

Happened on teams

Q1. Can you explain yourself and describe how you would manage a team of 10 employees?
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Round duration - 100 minutes
Round difficulty - Hard

The test had 3 parts:
1. Aptitude - 20 questions to be done in 25 minutes. (Medium level)
2. Technical MCQs - 25 questions to be done in 35 minutes. (Medium-Hard level) (HTML, JS, CSS, SQL)
3. Coding - 2 out of 3 questions to be done in 40 minutes. 20 minutes were allotted for each question. No switching between the codes was allowed. (1-easy, 2-medium in total)

Q1. 
Count Set Bits Problem Statement
Given a positive integer N, compute the total number of '1's in the binary representation of all numbers from 1 to N. Return this count modulo 1e9+7 because the result can...read more
Ans. Brute Force
The key idea is to count the number of set bits in each number from 1 to n and return the sum of all set bits.
 
The algorithm will be -
 
• For each i from 1 to N -
  • We find the number of set bits for each i.
  • This can be done using a built-in function (for eg builtin_popcount in c++) or by simply using a loop and left shifting the number and finding if the last place is set or not.
• Finally we store the coun...read more
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Q2. 
Smallest Number with Given Digit Product
Given a positive integer 'N', find and return the smallest number 'M', such that the product of all the digits in 'M' is equal to 'N'. If such an 'M' is not possib...read more
Ans. Brute force
A simple approach will be to iterate through all possible ‘M’ values, i.e., from ‘1’ to ‘2147483647’ (the largest value that a signed 32-bit integer field can hold), and check if their digit multiplication is equal to ‘N’.
 
Algorithm:
• Run a loop where ‘i’ ranges from ‘1’ to ‘2147483647’:
  • Set ‘CUR = i’. The current ‘M’ value.
  • Set ‘MUL = 1’. Use it to store the digit multiplication of ‘M’.
  • Run a loop until ‘cu...read more
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Round duration - 45 minutes
Round difficulty - Medium

It was the first face-to-face technical round. The medium was ModernHire. There was only 1 member in the interview panel. This round tested me on C fundaments, Operating System basics, and problem-solving skills.
Questions asked:
What are the TRUNCATE, DELETE and DROP statements?
What are void elements in HTML?
Define multipart form data?
1. How does the C compiler works?
2. What are deadlocks and why does it happen?
3. How to resolve deadlock?
4. What is a kernel?
5. How to dynamically allocate memory in C?
6. What is makefile?
7. What is multi-threading and why is it useful?
8. What is the need for synchronization in OS?
9. How do you run a program of 10 GB using 2 GB memory?
10. What are semaphores and mutex?
11. How is HashMap implemented?
12. Difference between linker and loader.
13. Importance of header files.
14. What is Dynamic binding?
15. What type of database should you use where transactions are involved?
16. Brief discussion on the Internship experience.

Q1. 
Merge Sort Problem Statement
You are given a sequence of numbers, ARR. Your task is to return a sorted sequence of ARR in non-descending order using the Merge Sort algorithm.
Explanation:
The Merge Sort...read more
Ans. Recursion
The basic idea is that we divide the given ‘ARR’ into two-part call them ‘leftHalves’ and ‘rightHalves’ and call the same function again with both the parts. In the end, we will get sorted ‘leftHaves’ and sorted ‘righthalves’ which we merge both of them and return a merged sorted ‘ARR’.
We implement this approach with a divide and conquer strategy.
 
Here is the algorithm : 
 
1. Divide ‘ARR’ into two-p...read more
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Round duration - 50 minutes
Round difficulty - Medium

This was a managerial cum technical round. I was asked to introduce myself (both technical details and hobbies). Then I was asked about my internship experiences and what I learnt from them. After that, he asked me questions about the projects mentioned in my resume. He tested my in-depth knowledge of the technologies that I used. He also asked me about the alternative solutions and the drawbacks of my solution.
After that, he asked me to speak about Operating Systems for 5 minutes without giving a pause. Then he asked me to speak about the OSI model and the TCP/IP model for the next 5-10 minutes again without giving a pause. He appreciated my perfomance and gave me a coding question.
What is User-defined function? What are its various types in SQL. What is an Alias in SQL?
Then he asked me whether I had any questions.

Q1. 
Find a Node in Linked List
Given a singly linked list of integers, your task is to implement a function that returns the index/position of an integer value 'N' if it exists in the linked list. Return -1 i...read more
Ans. Recursive Approach
The steps are as follows:
 
1. If the head is null, return -1 since an empty list will obviously not contain the element that we need to look for.
2. Check whether the head’s data is equal to the element we want to search. Return 0 if it is.
3. Then recurse on the next node from the head and get its answer.
4. If the answer from the recursive call is -1, your answer is also -1 since you already check the head’s d...read more
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Round duration - 15 minutes
Round difficulty - Easy

Typical HR questions were asked in this round.