Recent posts in Interview Experience

1.Introduction

2.B tech project

programming

1.program to convert decimal to binary.

2.again asked to write recursive code of it.

OS

1.how a new process starts after all the booting process?

2.asked about fork system call and exec system call.

3.Given a code snippet and asked what is the error in that.

4.corrected...and asked the output of that code.(the code is about the concept of fork system call)

5.asked about 'ls' command in linux and how it works, how it print the output to console.

6.asked about pipes.

7.and asked some synchronization concepts like communication between the processes, why we need synchronization, producer consumer problem.

and it took 30-35 min of time

Interview was scheduled in afternoon session, but in morning i got a call saying if i am available interview can be conducted in morning session.

Interview was divided into two portion, 1st was programming and 2nd was on the subject we had selected.

Programming:

They asked me to write recursive code for int to binary. And then asked me to modify the code for float to binary conversion.

[Before writing code for float to binary they asked to do that on pen and paper.]

Algorithm questions:

   1. What is spanning tree ?

   A. Explained with an example of electronics circuit and wire.

   2. If i am having ‘n’ edges will it be a spanning tree ?

   A. Said it will create cycle.

   3. How can you identify cycle in graph ?

   A. Said using DFS.

   4. They asked what is DFS and how it works?

   A. Started explaining the algorithm but they said just give the concept.

   5. What is minimum spanning tree ?

   A. Told 

   6. How can you find MST ?

   A. I said using Krushkal or Prim’s algorithm.

   7. Explain prims algorithm ?

   A. Explained it and discussed about it’s time complexity. I had said in it we use heap so the next question was on it.

   8. Why we use heap and not other data structures ?

   A. Said about time complexity and tried explaining but it seemed they were not convinced.

   9. Asked me about the property for which we us heap in prims algorithm.

   A. I said about finding minimum in log(n) time but they were asking for something else. [ It continued with awkward    silence. Later on it striked they were asking about decrease key operation.]

  10. Again they were back on MST and asked me if i decrease weight of edge then how to recalculate MST ?

   A. Said as it is in MST so decreasing weight of edge won’t change MST.

  11. Then they asked what if i increase the weight ?

  A. I said we can re-run algorithm. Then they asked me for efficient solution i said we can remove that particular edge which will result into two disconnected trees. Now out of the available  edges to connect this trees we can pick the minimum one. [ Was not much clear at the time of explanation. ]

  12. They asked me to prove why after this process the tree will still be MST.

  A. It seemed for me obvious and was not able to prove. 

IIT Madras MS CSE Interview

Date: 20-07-20
Time : 10:00 - 10:30
Panel 1

There were 5 people on call but only two interviewed me...

1st Interviewer asked

1) introduction
2) programming question
  String copy function
  - no.of arguments
  - implement without using library function
  - implement without using loop(recursive)
  - and explain above all with one example

2nd interviewer
Subject : Data Structure

1) Explain binary search tree
2) use of BST
3) speciality of BST
4) Balanced binary search tree
5) Given the number ,how to insert it in BST and what is its complexity
6) Explain all tree traversal method and what is the speciality of inorder traversal.
7) Explain Binary search and it's complexity,  solve it's recurrence equation

BLOG INDEX

• Interview Details and Stage 1 (Coding)
• Stage 2 (Home Interview)
• Post Result Talk with Professor (about CDS/CSA, DREAM LAB, Research)

Date – 10-July-2020, Duration – approx. +45min (Between 10:45 am to 12 am)

Stages – Two (Online Test, Home-Interview),

There was Online Google Form asking for Preferences, SOP (why you have chosen preference), Projects List, Professional Website (LinkedIn etc.), Programming Skills profile link.

(You need a background, possible experience to select labs, because they have your profile at the time of interview and ask questions why this lab, why not this)

Labs allowing to CS/EE only – DREAM LAB, MARS LAB, VAL, CSL.

---------------------------------------------------------Stage 1

It consists of Basic Objective Question based on Engineering Mathematics and Discrete Mathematics.

Syllabus – (source CDS brochure) – Combinatorics, Linear Algebra, Probability, Statistics, Differential Equations, Plotting, Data Structures and Algorithms

Platform – HackerEarth

Pattern – 7 Questions (5 marks each), 5 Multiple choice questions, and 2 programming questions

Programming Languages allowed – C (gcc 5.4.0), C++, Java.

Time: Early Morning 7:30 to 8:30 am ( then non-stop 45 minute online test)

----------------------------------------------( round brackets are showing my thought process () )

Q1. A group of 12 people, consisting of 6 couples, have reserved a row of 12 seats at a movie theater. How many ways are there to seat these people if couples want to sit next to each other.

Options – 46080, 23040, 1200, 479001600

(My Reasoning: 6 group permutation then each couple permutation - 46080)

------------------------------------------------------------------------------------ 

Q2. The plot of $y=e^{-x}sin(2x)$

(well I used calculator to put x value and get y value)

( I can straightaway delete the option c, for other I went raw method)  (anyone knows better method can suggest)

Q3. Consider the system of equations

$x+3y-z=4$

$4x-y+2z=8$

$2x-7y+4z=0$

Options – No solution, unique solutions, infinitely many solutions, None of the above

(I got last two rows same on initial first row operation)

Q4. What is the sum of diagonal elements of the matrix  $\begin{pmatrix} 1 & -1 \\ -1& -1 \end{pmatrix}^{10}$

Options – 0, 32, 64, 128

(Eigen Value coming out to be = ±sqrt(2)) ( in hurry, and in morning sleep I have done raw matrix multiplication also)

-------------------------------------------------------------------------

Q5. You are randomly selecting one of two coins A and B and tossing it. Coin A is fair but Coin B has ¾ probability for tails. If after the coin toss you observe tails, what is the probability that you had selected coin B?

Options = 0.5, 0.6, 0.625, 0.4, None of the above

(applied Bayes theorem)

Q6. Graph Traversal BFS

Say you are given a graph with n vertices labeled with IDs 0 to (n-1). The graph data structure is provided as an adjacency matrix G of size n×n. The row i of the matrix corresponds to the neighbors of the vertex ID i  in the graph such that if there is a value 1 in the column j of that row, there is an edge from vertex ID i to vertex ID j , and if there is a value 0 , there is no edge between vertex i and vertex j.

Given a source vertex ID s  preform a breadth first traversal (BFS) of the graph and print the IDs of the vertices visited. The traversal of unvisited children from any vertex should occur from the smallest to the largest child vertex ID.

Sample Input
4
0 1 1 0
0 0 1 1
0 1 0 1 
1 0 0 0
1

Sample Output
1
2
3
0

( code template was provided with necessary declaration, reading input in adjacency matrix, we have to write main code) ( i haven’t done this question)

---------------------------------------------------------------------------------

Q7. Frequencies of even and odd numbers in a matrix

Given a matrix A of order N × N, the task is to find the frequency of even and odd numbers in matrix.

You will read the input and write the output from/to standard IO (console). Sample template code to read and write from I/O is provided for C, C++, java. Choose one of the languages comfortable to you.

Input format:

The data type of elements of A is INT. You read the matrix A from the standard console input as explained below.

The first row has the value of N, which gives the size of A. the following N rows are rows of A, with each row having N integers separated by a space. There is a trailing space at the end of a line.

Output Format:

You should output integers which are number of odd (OO) and Even Numbers (EE) in the given matrix to standard console output

OO

EE

Sample Input
4
1 1 1 1
2 2 2 2
3 3 3 3
4 4 4 4

Sample Output
8
8

(Similar template code is given)

(it was simple, just have to check odd and even number then have to count)

-------------------------------

Takeaway:

1. Do programming after Gate if you are in safe side. Else do both programming and interview preparation.
2. Keep practicing mathematics. As an engineer always practice math. It will never leave as long as you are in engineering. In fact, entire computer is built on mathematics model (Turing machine).

Please utilize your B. Tech Time properly, Do Labs properly, read subject (at least try) from Std. Books and guide your juniors. If you have done B. Tech then please utilize your MTech time properly.

-------------------------------------STAGE 2 - Home Interview

There was waiting room and other main interview panel.

Platform – Microsoft Team

My preferences was:

1. Distributed Research on Emerging Applications & Machines (DREAM LAB)
2. Cloud Systems Lab (CSL)
3. Video Analytics Lab (VAL)

( Reason was background subject related to DREAM then IOT which I have little bit experience)

There were 4 professor, 3 male, 1 female. Out of which 3 have asked me questions. (Rest 1 was of V.A.Lab I think)

As far as I remembered (No visuals from there side, and short name were there) – There was Prof. Yogesh Simmhan, Female faculty Prof. J. Lakshmi. Rest I don’t remember name.

They started with reading my application, then my lab preference (why this or that), projects, gate score and reason for Gap in year. ( they asked me reason for VAL, I said I have read Image processing subject in my B.Tech and done some projects related to video manipulation)

(after Interview I have seen notification that someone viewed my LinkedIn profile at the starting of interview, as provided in form)

So, then They started: (I will try to format questions as they have said as best as I can)

-------------------------------------------------------

P1 (first professor): So, we will start with Data Structures and Algorithm. It is fundamental subject and should be known by all.

(Q1) Suppose, we have an array of ‘n’ numbers, I have to take min 10 elements, what should be the algorithm and time complexity.

(well I was not prepared for DSA, but every system subject but still I have given Gate, I know things right.)

[ I started with explanation of First sorting the array and then indexing array for first 10 elements]

P1: What is the time complexity of your process.

[told about using sorting algo – quick sort O(n.logn) and then indexing O(1)]

P1: Can you reduce the time complexity; can you think of it in other way.

[I started with some non-sense (I think greedy type, he pointed out my mistake) then in last I changed to naming unsorted array and using linear search for first element and then using it for 10 times, which will give time complexity as 10 times of O(n)

P1: Can you reduce it further.

(okay reducing more, think Vijay think)

[ I said we have to search an entire array at least one time to look for min element so it will minimum take O(n) time]

( they have given me time to think and come to solution)

P1: Topic changed

(Q2) do you know about sparse matrix.

(well I was thinking I have heard that name before and then)

[ it consist of minimum element like that]

P1: He immediately pointed out my mistake, and then said about sparse graph, using zeros and one in matrix.

( I got the link to area in my brain for that topic)

[ then I told about general adjacency matrix, zeroes for no edge, 1 for graph edge between vertex]

P1: okay great. Can you draw adjacency matrix.

[ drew graph then matrix and showed]

P1: now as we see for sparse matrix, it is taking more space can you provide alternate data structure.

[yes, I described adjacency list][ they asked me to draw and show]

P1: In sparse matrix, we have just 1 but it can be any non-zero value, right. So whatever data structure you have given can it provide such value.

[I said yes, and said it is linked list node, along with node and address we can have another parameter in that node.] [ they asked me to draw and show]

(now level increases.)

P1: Okay, great. Now I have vector of ‘n’ number and I need to multiply that vector with data structure you have provided. Like we do in adjacency matrix and matrix multiplication. Can your data structure do that.

[ Initially I asked him to explain one more time. Then I formulated first matrix multiplication. M as adj matrix and B as vector ( I asked vector to be column vector to support multiplication) then showed A(n*n) * B(n*1)

Then I took adj list data structure and …………]

( I know I have struck there but whatever my thinking process and direction I keep on explaining)

( there was google doc where I have to show him doing that)

[ I said we will traverse node by node, look for node number and then multiply it with that index in vector only)

( okay great, bolne ko to kuch bhi bol skte he, esa kr lo wesa kr lo, par ab bol diya ab kya)

P1: great. Can you construct the program for that in the google docs.

(I was like, seriously?? Right now?? I don’t know where all my programming skills have gone to may be still sleeping for morning routine) ( ham bhi kha haar maan le wale the)

[ I tried, started, got confused, got lots of question what should be struct data name, what is node name, what is node header. Then he said just right main programming construct, you know C. well okay. I again started righting adj matrix code but then changed to traversing the linked list code. Wrote few lines of loop. He said okay we can stop now.]

P1: asked another faculty member whether he wanted to asked me about video lab or not. He said not needed.

P1: then he asked female faculty to ask me about OS question.

( I was like, okay I know OS, I can do that good)

------------------------------------------------------------------ 

P2 (female faculty) : Vijay, do you know OS, how much have you read.

[ I said I have read basic concepts of OS and covered GATE syllabus topics]

P2: what is time sharing scheduling algorithm in OS.

[ I confirmed whether they are asking for Round Robin or not.]

P2: she said to explain it

[Explained arrival of process, ready queue, time quantum, preemption and execution till completion]

P2: Can you determine parameter by looking at that we can say the time quantum gives fair chance for every process or not.

(from now onwards, deep thinking process arrived)

[ I tried to explain her, having n number of process they will execute one by one ……]

She interrupted and explained what she is asking for.

[ I said we can calculate time quantum if we have given n number of process, context switching time, to allow fair share for all process]

She again explained that What is the parameter or ratio by which looking at that we can say that time quantum is fair for all process or not.

[ I told her about using turn around time, average turn around time to check if all process is executing efficiently.]

She asked what is turnaround time.

[ I told her basic definition]

Then she explained the effect if some processes are having large burst time or some having less. ( as far as I understood it was like convoy effect in fcfs type). She said how in that you can say turn around time will be that parameter.

[ now I have accepted my invalid point. I asked whether we can use some combination of waiting time or turn around time]

She again explained that she is looking for parameter by seeing it like if I say it is greater than 1 then we can say it fair or less than 1 not fair like that.

( now I was asking God for some help, to show some mercy and path to think, but God was busy fighting Corona)

[ Now I got stuck, completely blank, I asked for some hint]

How can you determine which process should execute or are waiting long enough to affect their performance?

[ meanwhile I said to her about using aging to determine priority whether they are waiting long enough or not required attention]

( I think aging is bit out of context for current question)

She said expected value or probability you can find for that.

[ I told about using burst time for calculation, then finding expected burst time and using that value as time quantum]

( yes I know, I was shooting arrows in dark, but I have to think right, If I stop then my brain will stop thinking at all)

She asked again how will you determine the burst time of process. Do you think process already have burst time before execution.

( I was like, well in gate question I have seen burst time before execution)

[ I was again started saying by seeing instruction whether they require cpu time or io time and calculating that, we can look for that instruction]

( I have seen expected burst time in SJF but at that as we are talking for round robin it doesn’t struck my mind)

She was like, how will you do that, suppose we have data instruction or require processing of the data in that case.

( I again chanted similar thing, looking for instruction and all)

She said suppose we are doing 3 by 3 matrix multiplication having large value of data it will take time. But again thing like we are having large matrix multiplication then in that how you will determine.

( I was like ohhh, ye kya ho gya, hamre jaal me hum hi faste jaa rhe he)

[ I said time complexity initially, but interrupted and then I explained my mistake and accepted it]

(She was nice, explained me properly, gave time to think, corrected my wrong thinking, In the end she was like smiling at my acceptance of mistake. And I was still thinking for some point to come back)

She said we should stop now, no problem and passed me to next interview.

---------------------------------------------------------------------- 

P3: do you know distributed system

[ I said I have read in B. Tech and explained working of Distributed system in short and RPC message passing]

P3: sounds great, so do you know basic synchronization concepts

[ I said yes for OS, but I don’t remember for Distributed system]

P3: yeah no problem. Concepts are same. It works like OS. So can you explain reader-writers problem

[explained about readers process and writer process]

He interrupted me asked me about synchronization problem involved.

[ I said 4 condition related to it]

He said okay. He asked do you think it gives equal chance to both reader and writer.

[ I said if we give priority to reader then writer may starve, or to writer then reader may starve]

Okay. Can you write the sudo code for reader writer synchronization solution in google doc.

[ okay, started writing meanwhile keeping on explaining whatever I was writing and why I was writing]

He interrupted me find mistake in my code where I have written mutex(x)….code…..mutex(x)

He said do you know semaphore and its function wait (), signal ().

[I immediately got my mistake and said sorry and corrected it down(x)….code…..up(x).]

[ meanwhile I was initializing binary semaphore x, but confused in spelling of semaphore or semafore.]

He said no problem in spelling just write rest of code.

( I was like why, here and now, what happen, even silly spelling mistake)

[I wrote all the code]

He asked suppose writer is in database and readers got suspended. Larger num of readers. So how they will resume their execution and in what order.

[ I explained about suspending list in semaphore and fifo way to wake up the process]

He further asked about priority in which reader and writer will be allowed.

[ I said if one reader is already entered into database then slowly all readers will execute first then writer may get chance]

P3: So do you know graph coloring problem. And its use?

[ I explained it in short manner of using it to color the node. And said I have seen its use in register allocation in compiler]

P3: can you explain graph coloring algorithm.

[ I said I don’t remember the algorithm, as I have solved question in rough manner and explained that manner of identifying large clique, using color and reusing them unless necessary.]

In the last he asked me whether I know programming or not.

[ I said I have done competitive programming 2 year before and from past 2 years I was focusing on Gate but I know basic programming.]

( and it ended, they disconnected me)

--------------------------------------------------------------------- 

Takeaway:

1. As I have felt, they were looking for how far I can think, because that OS question seem like research itself. How I formulate my answer and explain clearly. They were cooperative, giving time, explaining, correcting mistakes.
2. Basic Gate preparation will not help much, you have to pick up book and start reading out after Gate (if you haven’t). I have read OS for basic topics but still you have to try.
3. I was calm and trying to think hard for solution but still at that moment it was just not coming up. So, it is very much necessary to answer properly. Practicing how you will give the answer, starting from basic point to slowly increasing level with clarity.
4. At least revise all your short notes once after Result and practice math.

If nothing happens, you don’t get selected no problem, you got chance and experience. You can improve further building on it;.

Result: declared in the evening, got mail in morning. Selected.

GATE Score – 807, EWS

---------------------------------------Post Result Talk

Next day Prof. Yogesh Simmhan (Dream Lab) called me for this good news, my performance and discussed about its lab, department preference I can change if I want, what they will do in lab etc.

• He asked me whether I have visited the lab page or profile page and I am interested in it or not. (dream lab was my first preference and interview was little bit about that)
• About Lab – He said Lab overall works on Distributed System. Every few years idea of distributed system keeps changing, new technology emerges, and last few year IOT has been on emerging areas that is expanding. So we have multiple projects going on IOT, some of the newer ones have to do with how can you, for example, make use of Raspberry Pi class device, can be deployed as a part of smart cities, even for example Drones, we have projects coming around drones. IISc has new center on Autonomous computing that’s coming up, so for that we are trying to examine how drones, these flying platforms can we seen on as computing platform. We think of drone as flying platform, but to me a drone is nothing but a mobile phone (with flying capacity). So, we have mobility aspect of it and we also have sensors sort of video camera and so on that are modeled on the top of phone and flyer on.
• Some of Problems we are looking at how can you actually do some of the computing at the top of say video streaming, maybe even doing some deep learning …. So on, on top of the drone platform itself. And then there is some system aspect of it so how do you tradeoff between parallel computing on top of the drone itself as energy efficiency, right because drone has only captive amount of energy which you can use for flying and computing. And if you do too much computing, you might actually reduce flight time and so on. And how can these drones actually do task co-operatively, not just observational task even computing task co-operatively. So, can you actually move data from one node to another and then sort of distributed computing, you can think of flying Hadoop cluster right, as what drone could be considered as. Lot of interesting problem around IOT and drone computing like we are starting to look into. Some of these also have lit bit flavor of Machine Learning and Application domain for us because of anywhere and everywhere. (So, it is kind of thing you will be interested in?)
• Interest - One thing I can set of tell you is that one way to think about since you applied for Research program, it is not course program, right which means that the lab that you join is way more important than the department you join. Research student take typically one semester of course, and three semester or almost one and half year is spent in research lab doing research. Courses can be taken in any department, IISc doesn’t restrict you saying if you join a department A then you can only take course from A. In fact, many of my students take courses like operating system in CSA department. It is very flexible. What really matter is the research lab you join and the kind of research you do. That is why maybe doing little bit of homework on that and understanding what your interest are would be helpful
• Department – One thing I can tell you is system department in computer science typically looks at more classic computer system perspective like architecture and operating system. They are parallelly good at it. (some professor name). what the CDS work on the newer system like cloud computing, big data platforms, IOT, and so on. So that is the set of difference. If you like classic operating system and you like to work on Linux kernel and so on something like CSA might be good. If you want to set of do the next higher level, if you want to see like how tens of hundreds of distributed systems could be working co-operatively together to solve emerging problems. Things like edge computing drone computing didn’t exist five years back and cloud computing didn’t sort of prevalent ten years back. But we use fundamentals idea about operating system because at the end of the day your synchronization primitives are going to be similar whether it is one-two thread on single processor or across hundred machines across a wide area network, in terms of memory you will be going to network for coordination and so on. That I would say is set of key difference between some of the CSA based systems lab and the CDS system lab. (that is why think about it)
• Department Preference – what IISc will do is IISc will give only single offer based on department priority that you have chosen. They will not give choice to you, let say both CSA and CDS are willing to take you. If one department is higher choice you only get a single offer from that department, and if you decline it, it is declining entire IISc offer. Now you have chance to speak with faculty at both CDS and CSA, so do a little bit of homework and if you strongly feel that something at dream lab will be right lab for you. You have time till Monday to change department preference. But do look through the lab because that’s going to be like I said critical part, what does the actual area you want to work on and based on that You should chose your department where that lab is present.
• Advisor/LAB – I would be one of your primary choices and even within the department since you have given the priority order, we would sort of respect that, but we also encourage to talk to couple of other labs, so that you enough information and choice is up to you. If you are interested in dream lab at CDS, I will be happy to take you (based on performance in interview and resume). I think you have one month after you join to finalize your lab after you join the department. It is two-way street, both the lab must be interested in you and you must be interested in lab, if both of these happen, then you will be able to.
• Students/Research – way we do interview we want to understand the overall skills of the student because research itself is such a fast-moving area, we don’t want to hire someone who has narrow set of skills. At the end of the day we do not expect student to be set like sort of extremely talented when they come but must have sound fundamentals and they should be really passionate about what they wanted to do. Because it was like what Edison said Innovation is set of 99 percent perspiration and 1 percent inspiration. As long as student willing to work really hard, they enjoy what they are doing and they are interested in system research. IISc or Lab or Department will provide the right environment for you to thrive. Sometimes student design their own projects and they come in and say this looks nice but I wanted to do something related to this. That way you can carve a whole new topic for yourself, that is the kind of flexibility we offer. Research is not like a production line; it is not a kind of algorithm that you follow. Research is all about creativity, trying to find about very interesting problems and trying to solve that to the best of your abilities. All the students and faculty are hardworking and they expect a lot. The reason we are able to compete with some of the top 100 university in world is not just because we have right students but we have hard working students.

Thank You for Reading. Hope It helps. Constructive Views are welcomed.

Date – 06-July-2020, Duration 43-45 minutes (2:45pm to 3:30) (online using Google meet platform)

There was one seminar before the actual interview to familiarize the candidates with the process and area. We have to write our preferences in Google doc shared 5-6 days before.

Background Subject – Computer Organization, Operating System.

Research Sub-areas – Database, Operating System

Started with presenting my application profile, then asking basic question related to year gap, and Gate Score.

Asked about preference between Database and Operating System. (I said I like both)

Prof. Deepak D Souza was coordinating between faculty - Prof. Vinod Ganapathy (asked question for OS), Prof. R.C. Hansdah (Database), Prof. Matthew Jacob (computer architecture).

(I will try to frame questions as exactly as they said, and will give gist of answers I told, as thinking and presentation skills are different for different persons)

---------------------------------------------Started with Matthew Jacob Sir.

1. Can we represent any real number in computer?

[Told about floating point IEEE 754, or rounding techniques involved, range involved and if some are number are not able to represent then we have to round them.] [ that is not any but within range]

2. What is the format for IEEE single precision format with subparts?

[Told with proper explanation and showed the picture also.]

3. How do we do floating point addition in computer.

[Told about normalizing result and adjusting exponent.]

4. Can we pipeline the floating-point addition?

[Yes, initially i didn’t understand then he asked about pipelining]

He got disconnected midway and couldn’t join. (may be network problem)

-----------------------------------------------And Vinod Sir took the command.

He showed slide pictures and asked basic question on it.

1. Showed the slides, Picture was like

      int p = 1234;           // (some number)
      printf(“%d”, &p);

1. How printf works.
2. What is the role of OS?
3. What is system call. What does it do? we have library file where printf code will be there, so how does system call work

[ I started with explaining system call behind the printf() function, then he asked question mentioned above ] 

((he asked if have printf working code in library file then why we need system call, since printf code will do the work))

2. Showed next slide

     printf(……)
     {
      // implementation of printf
     }

1. How system call is different from normal function call. (again told about OS, security and system call)
2. What exactly it will differ in hypothetical OS.

 (told about user mode, at that point I understand what I have to say in previous question, he immediately asked me about how user mode will be converted to kernel mode. I said there is bit. He said who change it. I said OS. He said How. I was not knowing at that time)

3. Showed one more 

running the both code in uni-processor system.

//code 1
[p1]  int *p;
[p2]  p = 12345566h ;    // some address
[p3]  *p = 1;
[p4]  printf(“%d”, &p);

//code 2 
[q1]  int *q; 
[q2]  q = 12345566h;    // same address
[q3]  *q = 2;

1. What will be the output when it runs parallel in the uniprocessor system? (told about race around condition)
2. Which line would require the OS help? (confused about p3, told about p1, p2, p4)

---------------------Jayant Sir was not present so, database question was asked by RC Hansdah sir.

1. What is the definition of relation in Relational DBMS? (told)
2. What is mathematical definition of Relation? ( I got confused I said I don’t know, I haven’t read. But after interview I think I could have said relation definition I studied in Discrete Mathematics)
3. What is candidate key, Foreign key, Primary Key?  (told)
4. Difference between Primary Key and Foreign Key? (told)
5. What is transaction?  (told)
6. What are the properties of transaction? (told about ACID property)
7. What is 2pl locking protocol? (told about its two phase and working)
8. How does It maintain the serializability? (told how 2pl block transaction requesting for conflict resource)
9. What is 2PL commit protocol? (I haven’t read about it, so told doesn’t know. this protocol is related to distributed system)

In the last they asked about if I am having question and It ended.

Result: declared shortlist on 14-July-2020. Not selected.

Score: 807, EWS

Takeaway:

• I think I should have clear priority of subject I have chosen. It gives them idea on my research interest.
• Apart from OS, I have been asked basic question. But for OS, I think if I have taken a deep breath and then answered the question, it would have helped me to present my answers beautifully. 
• System Call, BIOS working, some topics required reading books apart from Gate preparation.

I have read “Principles of Operating Systems” book by Naresh Chauhan. I liked the book as it has all the basic content.

BLOG INDEX

• Interview Details, Experience & Result (to get comfortable with environment)

• Takeaways From Interview Experience (to learn from experience)

• Information Related to SysAdmin Position (know about your RA position)

• My views on SysAdmin RA and TA

• Why I have chosen SysAdmin RA (what is your reason for chosing)

----------------------------------Interview Details, Experience & Result

It was round 1 for top candidates applied and round 2 was after 5th round of COAP for remaining candidates (based on seats vacant in round 1 and does not accepted any offer)

Date: 22-June-2020 (online using Google meet) (due to COVID-19)

Position: CSE Sysadmin RA (6)

Duration of interview was 25-35 minutes. (after 1 pm)

There was a waiting lounge using another Google meet. I was waiting at position 8th in panel 1. (around 10-9 members in both panels)

There were about 4-5 panelists including one professor (Prof. Varsha Apte), Sysadmin head (Mr. Ranjith Kumar) and current sysadmin RA.

(I will try to frame questions as exactly as they said, and will give gist of answers I told, as thinking and presentation skills are different for different persons)

---------------------------------------------

I1(Varsha Apte): Say Your Name, Form Id, and Declaration that nobody is helping me in this interview, and haven’t selected any offer.

[Told]

I1: Let’s start with introducing yourself to your panel members. Start directly from your college experience.

[told college name, work done, competitions participated and other experience.]

       I1 transferred the command to I2 (Ranjith Kumar)

I2: What are the Operating Systems you used?

               [told about Windows and Linux in college]

I2: Any Linux operating System you used?

               [Ubuntu 14.1, Fedora 13]

I2: What are the commands you remember?

               [ told all commands I remember group wise right from starting terminal then other]

I2: How can you count number of files in a folder?

[I told I don’t actually remember the command but we can do using ‘ls command’ plus other. Or we can write script using if-else condition checking file]

(( we can do “ls | wc -l”  or using find with some parameter, or iterate every file and check if it is file or directory ))

I2: Difference between Ubuntu and Fedora?

               [told about apt-get and yum and then community response etc]

-------------------------------------------------

I3: What does ‘top’ command do?

               [ told it worked like task manager in windows, then told some details]

I3: How to see network status?

               (I actually didn’t get the question initially but then told what I know about some network commands)

I3: How to connect with different system?

               [ using ‘ssh command’ we can access another computer terminal]

I3: Since you have used ‘vi’ editor, how to go to last line in a file opened using ‘vi’ editor.

               [ I told I don’t remember, there are commands visible in ‘vi editor’ to use.]

----------------------------------------------

I4: How can we connect to different system? Explain.

               [explained about ssh command]

I4: How can we execute two commands simultaneously?

               [ using && or pipe command]

I4: How to write to a file without opening it.

               [ using >> right shift operator to echo output to file]

I4: What are the ways to find/search a file?

               [using find, locate, grep with name ]

I4: How to end a process when you see in output of ‘top’ command or when it gets hang?

               [ told about getting id from ‘ps’ command then and then using kill command]

-------------------------------------------------- 

I1: Do you know basic networking, subnetting etc?

               [ told yes and my experience of network handling in college using pfSense]

I1: What is the NAT? How does it work? How to distinguish two system with same port accessing same site?

               (( Initially started with NAT description and then using table, explaining private or public ip))

               (( things got stuck when she asked me about how NAT will distinguish between same request of different computer with same port. I told using table writing MAC address along with all details. But she confused me when request is served back from server to client and in Ip packet we will be writing MAC address of main router))

I1: What are the TCP Congestion Policies?

               [told about rwnd and cwnd, slow start exponential algo, AIMD and then detection. After detection back to slow or AIMD.]

I1: What are the difference between layer2 and layer3 ?

               [ told differences in terms of devices, mac and IP, etc.]

I1: What is the layer 2 protocols?

               (( I got confused, I was not remembering exactly what to told, she gave some hints but I was not able to say))

Result : declared on 7th July 2020. I was Selected.

Gate Score – 807, EWS

----------------------------------------------TAKEAWAYs

1. After Gate, please revise basic Linux commands and basic scripting (search in Google for important commands), commands related to networking. Linux and windows differences, problems. It is good to refresh your Linux memories even you get selected or not.

2. Revise ‘Computer Networking’ subject and watch videos for practical working of some basic protocol if you are not able to visualize. For other subject like OS depends on panel.

3. If you do not remember exactly then at least say what is in your thinking in that concept, how you are visualizing. Accept your mistake.

4. Although this year (2020) there was no programming test, but be prepared for that.

5. Still having doubt, then read their requirements, understand important topic. Visit their head page, RA page. Mail them.

I have read “A Practical Guide to Linux Commands, Editors, and Shell Programming” Book by Mark G. Sobell in college for Linux. I have googled out basic important commands to refresh my memories.

----------------------------------Information About Sysadmin (outsourced from RA)

• This year 2020 there is new program MS by Res. But it is open for TA and RAP category people only. That means RA would not be allowed. (if you are thinking to join)

• This is RA position (Institute RA) where you have to invest your time in CSE Lab under Sysadmin head.

• Officially it is 20hrs per week. Less in first year. More in second year (more work). Third year you would be busy in MTP (Major Thesis Project). However, mostly it stays below that but can get over the limit in rare cases ( Load is variable). Therefore, until you do your seminar and presentation you will be doing RA duties.

• Work is mostly systems related. Like maintaining CSE infrastructure like the Mail server, DNS server, L1/L2 networks, biometric system, LDAP, GIT and networking infrastructure. Deploying new services and ensuring security of such services.

• This is different from IISc RA or MS in other institutes. First it is exactly of three years called MTECH – RA (not in 2-3 year range). Second no thesis advisors would be assigned from beginning (in RA). Institute RAs (CSE Sysads and CC sysads) are free to choose any faculty advisors in any field. Although there is limit on faculty for number of students they can take and there are criteria of CGPA also.

• Stipend year wise is 13.4k, 14.4k, 15.4k

• You will not be spoon-feed but seniors will be present to guide you (as they said) and you will never be given more than you can handle

• Guidance, Meeting and all depends on guide.

---------------------------------------------------My views

It is still MTech but with 3 years. Just your friends will get the degree before you get.

So  

1. if you don’t have any other options (like TA)

2. you really wanted the IIT Bombay name

3. doesn’t know your research area yet or wanted to explore. (applicable only for Institute RA)

4. interested in Linux and programming

then you can prepare for it (Institute RA).

What TA have to do in first year you have to do in two year (+1 for Major MTech thesis). That means less workload or pressure, you can explore and learn in your pace. Enjoy Bombay life one more year (subject to coronavirus relaxation).

(well if you consider it as advantage then it can also be considered as disadvantage if your main goal is placement whether it is 2 years or 3 years, you have to spend one extra year. TA have 8 hrs. per week load. And they will learn to efficiently manage their time in this competitive world. And some have published the paper even in 2 years duration.)

-----------------------------------------Why I have chosen sysadmin RA?

Well, it was the closest which I can relate to my past experience. (next was CC sysadmin).

I have spent my last two and half years of BTech in computer lab of my private college. I have been developing projects for my college under HOD or Director (I wish I would have practiced competitive programming). From third year I have managed the entire networking of college using firewall pfSense (learning through documentation or videos) and then incorporating it using college management system we made (me and my friend) using radius database and captive portal.

Even I have installed windows 7 and Linux in each 100+ old poor computer system. I got to know some problems of dual booting, partition, correcting errors, sometimes exchanging RAM or Hard disk of system to get things done etc.

I even tried every Linux at that time (ubuntu 12, ubuntu 14, kali Linux, fedora 13, fedora workstation, centos, redhat developer version, linux mint). I even tried to boot MAC OS cracked version in one of the computer in Lab (well it didn’t workout but worked in virtual system)

That is why it was my first preference. Similarly, you should choose based on your work experience and interest.

Second was I wanted to be Bombay having dreams like other and at my score TA seems difficult. Moreover my EWS certificate was getting delayed as last date for application was approaching.

Thank You for Reading. Hope It helps.

The cutoff for an interview call was 845, for GEN category.

Before the interview, there was a 45 minute test – it had 5 MCQs and two programming questions. The MCQs were:

1. Identify the graph of sinx*log(|x|)
2. If we select a number from the first 50 natural numbers, probability that x + 96/x > 50.
3. 6 distinghuishable balls, 3 boys, make sure each boy has at least one ball. No. of ways?

and two more simple linear algebra questions.

The programming questions were – traverse a matrix in spiral order, traverse a matrix and find out frequency of odd and even elements.

Now, my preferences in the dept were CSL, MARS and DREAM lab, in that order.

My panel had three people – Prof Satish, Prof Yogesh and Prof Lakshmi and the interview began:

Panel: So tell me what do you mean by a sparse matrix?
Me: Told.

Panel: Okay, how will you store a sparse matrix?
Me: [I was pretty blank and discussed for a few minutes before giving up]

Panel: Okay tell me, which is a better way of representing a graph – matrix or list?
Me: It depends on what are the operations that you want to perform on the graph. For something like a BFS, a list is better.

Panel: Explain BFS’s time complexity in both list and graph.
Me: [Done]

Panel: Okay, suppose I am given a set of vertices and I want to check if it forms a path, which would be better?
Me: We could use a BFS to find the path between the vertices.

Panel: No no, we are given the list of vertices, we need to check if it forms a path or not.
Me: A matrix would be better, since we can look up if an edge exists in constant time or not.

Panel: Okay, if I give you p vertices, what would be the time complexity?
Me: We’ll have p queries, each of O(1) time, making it O(p).

Panel: Okay good. How would it work out for a list?
Me: If the lists are sorted, we can find if a neighbour exists or not in logp [I think it was incorrect – binary search cannot be applied on a linked list, but he didn’t seem to mind for some reason], so overall can be done in plogp.

Panel: Okay, if it’s not sorted then?
Me: In the worst case, we might have to traverse till the end of the list.

Panel: If I give you the average degree of a vertex is d, then?
Me: On average, the time complexity would be O(dp)

Panel: Okay, we’ll switch to OS now. What do you know in that?
Me: Virtual memory, synchronisation etc.

Then the ma’am asked very basic questions on virtual memory – what is virtual memory, why do we need it, how does an address translation work, who does it, how are the bits divided, what happens on a context switch, where is the page table base address stored, how does multilevel paging work, what is the advantage of multilevel paging and so on. Overall, quite basic questions.

Next they moved on to synchronisation – the prof asked me to solve readers-writers problem. I was given a Google Doc where I wrote code. The prof then asked a minor variation – suppose we only want to let x amount of readers enter into the CS, how would you do it? This lead to a discussion on counting semaphore, locks, how locks are implemented using TestAndSet, granularity of locks, efficient lock usage and that was it.

In the end, they asked me if I had a MTech offer, to which I said I do, but I am interested in research programmes and it’s only a backup. Then they said why not apply for a PhD and I said I am not sure right now, but would convert from MTech to PhD if I like it. 

That’s all, lasted around 45 minutes on Microsoft Teams.

Verdict: They had received around 2500 applicants, they selected 17 PhD and 7 MTech in the shortlist. Don’t know how many will get converted to final offers. 
 

IITD MS CSE Interview Experience.
 

There was a programming test before the interview – 5 questions, Codechef style. Here are the questions:

https://docs.google.com/document/d/1Okxf7GKKIuoxLUZzmNfVsAIv8EDaUrtXTwzT_8L27Es/edit?fbclid=IwAR0fugnsW9-Gb4tCzNCUa0fuim1BzOSoa_BQIQ0FSTjYBwXUTZAwSB9T3VA

Out of 300 odd people who appeared for the test, 80 were shortlisted for the interviews. I managed to solve two problems completely (200/500), and my rank was 31 out of the 300 odd people and hence was called for the interview. 




The meeting was on Microsoft Teams, they had said they might call anytime between 3 pm to 5:30 pm. My turn came around 4:15 pm.

There were 8 professors, out of which 4 asked me questions. They were:

Prof Smriti Sarangi (CompArch), Prof Sorav Bansal (Compilers, OS), Prof Priti Ranjan Panda (Embedded Systems) and Prof Subodh Kumar (HPC, Parallel Programming).

They read out my bio, my interests (Computer Architecture, Operating Systems) and started asking one by one.

SS: So you're interested in COA, what all topics are comfortable in?

Ans: Sir, caches, pipelining, performance metrics etc.

SS: How do you define performance? How is it related with frequency?

Ans: Performance is inversely proportional to execution time, but in overall performance frequency is one component - we need to know insts, CPI and frequency - which I elaborated with the standard equation.

Then he asked me a bunch of questions related to pipelining (how do stalls affect CPI, how do you mitigate them,etc etc), which I don't remember as they were mostly extensions of one question after another.

SS: Okay, if I want to increase performance, what's stopping me from using a 1000 GHz processor?

Ans: Sir, if you increase the frequency, the amount of time will decrease so in a small unit of time, I guess much work can't be done. It'll also lead to increase in power, for which you'll need an efficient cooling system.

SS: Okay, your answer is 75 % right. What else could be the reason?

Ans: [Thought for a while] Sir, latching would be a problem too. In too small a clock cycle, you won't be able to latch to take it from one stage to another.

[He was satisfied now.]

SS: Okay, suppose you have a computer which only has a processor and RAM, can you still make it work without a disk, from some other computer's memory?

Ans: I said yes sir, I've read about how you can remotely boot an OS so in a similar way, maybe we can use a protocol which might allow you to access the data from a remote location.

SS: Yes, you are correct. Such a protocol exists and it's called RDMA.

SS: Okay, I'll ask you one last trick question, just say yes or no, don't elaborate - suppose you have infinite physical memory, do you still need virtual memory? Ans: Yes sir, because we still need isolation which is an important component of modern day OSes.

SS: Okay, elaborate that [wtf? you said don’t elaborate] Ans: Then I explained him VAS, PAS and all that stuff.

Next, Prof Sorav started asking questions. He asked a bunch of questions about how the page table, cache and memory interact with each other, which I was able to answer well. Then he asked some convoluted question, which I think I was unable to understand properly as I gave him some other answer, then he realised okay I think we’re not able to get through the question properly.

SB: Have you heard about huge pages? What are they?

Ans: Yes sir, huge pages are used when you need pages which are much larger than 4 KB or the default size. Linux uses something called as THP (Transparent Huge Pages).

SB: Okay, can you elaborate what is that?

Ans: Sir, the TLB stores VA-PA mappings and since it’s a cache, it has to be small. But at the same time, we want to increase our TLB reach, so that we have lesser thrashing of the TLB itself.

As I was further explaining, he stopped me and said Okay, I’ve got the answer that I need.

Then Prof Priti Panda.

PP: You mentioned critical path somewhere when we were talking about caches, can you elaborate what is that?

Ans: it’s the path which takes the longest time to execute in a circuit etc etc.

PP: Okay, so suppose we need to formulate this is a problem and design an algorithm to find the critical path, how would you do that?

Ans: I was a bit stumped, and suggested some methods, then I asked if he wants a particular data structure to which he said yes, then I said maybe we can use graphs sir where the nodes are the gates and the weights of the edges are the timing delays of that particular gate.

PP: So do you mean all the outgoing edges of a gate will have the same delay?

Ans: Not sure, but I guess yes sir.

He didn’t seem much satisfied, but whatever, he said I am done and we moved on to professor Subodh. He only asked me one question - given a BST and [a.b], how will you print all the numbers between it? (yes, the same GATE 2020 question.) We had a 10 minute discussion on it as I knew the overall approach, but not the fine details of it.

And that was it.

Overall, it was an okay interview - I guess average. Some questions were hit, some were miss.

They did ask me which subjects I was interested in (could be also because I had talked to Smriti sir before the interviews and he had told me he’ll ask me CompArch)

Category: General 
GATE Score: 779
All India Rank: 312

This year the interview process was online due to the COVID-19 outbreak and the cutoff for getting shortlisted for interview was 776 Score (AIR 335) for General category. I interviewed for CC sysadmin RA.

[A day before the interview they asked for our resume and any projects we would like to show to the interview committee]

There were 5-6 interviewers, they first asked about my favourite subject, I said 'Computer Networks'.

Then, they asked basic questions like difference between switch and router, IPv4 and IPv6, frequency band of WiFi, routing algorithms, What is Google OAuth?, etc.

I was able to answer them but 2 to 3 times they had gone too deep like security in IPv4 and IPv6, VLAN, which I wasn't able to answer satisfactorily.

Then, as I had done internship from IIT-B last year, they asked about my work and my experience.

The interviewer laughs and says, “Do you even know how IIT Bombay network works?”
I said, “Yes, I do.” and explained them how the hostels and departments are connected, the campus network forms a private network, and all the packets to the outside (global Internet) are routed through a NAT router. 

The interviewer said, “Yes, good”

Now, comes the interesting part...

[I : Interviewer, M : Me]

I : Which operating system do you use?

M : Sir, I use Ubuntu as a dual boot.

I : Which is the other operating system?

M : Windows 10

I : Which OS did you install first?

M : Windows 10

I : Why?

M : Sir, because I wasn't aware of Linux in my first year

I : What will happen if I install Linux first and then Windows 10?

M : [...after thinking about 5 to 10 seconds...] Sir, I think we have to reconfigure the bootloader

I : Yes, correct

Personally, I think at this point the whole interview turned around in my favour.

Then, they asked whether I know Perl Scripting, Bash scripting, Python scripting, and Web development. I told them I know only the basics of bash scripting and basic python programming and I've done basic web development like HTML and ReactJS.

After this, they asked about my interests, I told blockchain and compilers. They asked if I'm interested in security, I said 'yes'.

Finally, they allowed me to ask any questions from them, I asked "Is there any scope of research in this position?", then they explained for 4-5 minutes that on some security related aspects it is possible, and in other fields it is always possible.

The interview lasted for 25-26 minutes.

Verdict: Selected 😊

I will be joining IIT-B RA as it seems to be the best option for me, feels like a dream come true! 😇

My tips to future aspirants about cracking RA interviews:
Personally, I feel that these interviews DO NOT require any preparation but reading interview experiences and asking the seniors helps a lot to get familiar with the process. They test how much you have played with computers, how much do you know practically. So, my advise to all the engineering students is that please utilize your 4 years, always keep experimenting and be aware of the practical things, that’s the only thing that matters (and yes luck is also a factor, but don’t worry about it as it’s not in your hands).

I would again like to thank @Arjun sir for providing this wonderful platform and for the Facebook group which gave me hope in February that it is still possible to get into your dream college through interviews 😀

I-Interviewer, M-Me

I- What is your research interest?
M- Deep Learning, Machine Learning to some extent and Brain Sciences.

I- Draw the graph of y=$\frac{1}{(5-x)}$

M- Drawn ( take the mirror image of y=1/x graph across x-axis and then shift origin to
x=5, i.e., shift the graph 5 units forward on the x-axis.)

I- Tell me the role of double derivative in calculus?
M- It tells the rate of change of derivative(first derivative), if it is +ve, that means the
derivative is increasing which happens at a local minima point in a function, if it is -ve
we’ll reach a local maxima point.

I- How will you extend this concept to higher dimensions, like if z=f(x,y), then how’ll
be the double derivatives work?
M- Sir in that case we’ve to calculate partial double derivatives such as

(I meant to calculate the above) and check for particular conditions (which I didn’t remember but could possibly be
“Second Partial Derivative Test”) to see if it is a maxima or minima.
(‘I’ not much satisfied)

I- What is the derivative of a vector w.r.t. another vector?
M- couldn’t answer.(maybe the solution is a Jacobian Matrix.)

I- Do you’ve idea about gradients, like how are they useful in Machine Learning or in
general?

M- (possibly gave wrong answer ) Gradients help us to determine shape of the curve
which would help us to know maxima or minima and help in optimization. (‘I’ not
satisfied and cross questioned about what I said but I wasn’t able to elaborate and was
musing)

I- What is the role of Eigen Values and Eigen Vectors like in Principal Component
Analysis?
M- I haven’t digged deep into the maths of ML/DL but worked with the coding part.

I- How do you calculate Eigen Values and Vectors?

M- We solve $|A-λI|=0$ for Eigen Values and $\text{(A-λI)}\text{X=0}$ for Eigen Vectors.

I- Give an algo to find rank of a matrix?
M- Convert to row Echelon form, and then check number of non zero rows, basically
the number of independent rows.

I- Is row rank equal to the column rank, what is the proof that the row rank is equal to
the column rank?
M- Yes they are equal. Couldn’t give the proof.

I- Have you read anything from systems like OS etc?
M- No sir.

I- How will you store a sparse matrix?

M- Will store in a linked list, for every row a central node connected to all non zero
values in that row. (like a sparse graph stored in an Adjacency List)

I- How can you store them in an array?
M- didn’t remember(but the answer would be possibly using each non zero element as
a tuple (row, column, value) and store them in a n$\times$(no of non zero elements) sized
array.)

I- Suppose I’ve a polynomial of very very high degree, how’ll you store them?
M- Using linked list.

I- Can you write the structure of that linked list node you’ll use in that case in C?

M- struct node{
int coeff;//coefficient
int exp;//exponent
Struct node* next;//pointing to next higher degree of the polynomial
}

I- Suppose you’ve an m-ary complete tree with n nodes, what’ll be the height of the
tree?
M- $log_mn$

I- Create a BST from keys 10,5,4,20,15,11,30, tell me the number of levels and height?

M- Height=3

I- How’s the height 3 and what’s the number of levels?
M- Max root to deepest node distance is from 10 to 11 and no of edges in between is 3,
so height=3, No of levels=4, level 0(10), level 1(5,20), level 2(4,15,30), level 3(11).

I- What’ll be the avg comparisons to find a key in that BST?
M- approx 2.
(1 comparison to find 10, 2 each for (5,20), 3 each for (4,15,30), 4 for 11,so
avg. comparisons = $\frac{1\times1+2\times2+3\times3+4\times1}{7(total\text{ }elements)}$ = $\frac{18}{7}=2.57$)

I- Show me the exact fraction that you got?
M- $\frac{18}{7}$( ‘I’ satisfied)

I- No of BST possible with ’n’ keys?

M- $\frac{ \binom{2n}{n}}{(n+1)}$ Catalan Number

I- So you mugged it up, tell me how it is derived.
M- It is derived from the below recursive equation, suppose I choose a particular key
for root, now among (n-1) keys left, select ‘x’ keys for the left subtree, (n-1-x) will be
left for the right subtree, let T(k) denotes the no of BST possible with ‘k’ keys. Then,
$\text{T(n)} = \sum_{x=0}^{n-1}\text{T(x)}\times\text{T(n-1-x)}$.

I- Expand the expression for n=2 and 3.

M- T(2)=T(0)$\times$T(1)+T(1)$\times$T(0)=1$\times$1+1$\times$1=2
T(3)=T(0)$\times$T(2)+T(1)$\times$T(1)+T(2)$\times$T(0)=1$\times$2+1$\times$1+2$\times$1=5
I- Ok, we’re done.(Interview ends)

(P.S. — My interview lasted for around 30 minutes. I might have missed some
questions, and the above portray the picture of what I could remember, vague or exact.
I personally feel that they put so much emphasis on Calculus and Linear Algebra
because of my research interest being Machine and Deep Learning. They spent quite
significant time on my research interest rather than on just GATE subjects basics, so
basically you’ve to brush up in depth and read more and more proofs on concepts in
basic CS subjects(Data Structure, Algo, Engineering and Discrete Maths, OS,
Architecture etc.), read your research interest well, and good amount of mathematics,
starting from higher secondary to graduation level.)

Giving my two cents hoping that it would help someone later. This years procedure was a bit different. Due to the coronavirus pandemic there was no written test but a direct interview. Unfortunately this years GS cutoff for receiving an interview letter was pretty high, probably because they had to cut out the written test round. The interview was an online interview. We had to fill out a form regarding our preference list of the RA projects available. I chose IBM AIHN Project[NLP], Abdul Kalam Fellowship Project on Medical Informatics and Academic Office (SAFE) as my top 3 choices in that order. The interview was scheduled on 22nd/23rd June. By 20th June I received a mail saying that I have an interview for SAFE on the 22nd. The interview was held over google meet. This is how the interview went,

Interviewer – I

Me – M

I: (Mentioned a set of rules i.e. no looking up answers, no one else in the same room to help out etc. to which we have to agree for obvious reasons)

I: What is your GATE score

M: told

I: Tell me about your academic background

M: told (college graduated from, cgpa, goals etc.)

I: So you had graduated in 2019. What have you done in the past 1 year ?

M: told

(Note: They had informed us to provide a shareable Google drive link containing our CV, project reports or anything we would like to show the interviewers. I gave my CV, two project reports and my research paper)

I: I see that you have worked on a Bluetooth based attendance system (SAFE was also an attendance system amongst many other things). Can you explain a bit more about it ?

M: Explained in detail

I: Do you have any skills such as C, Java, Django, Android etc.

M: Told them that I knew C,Java, Android basics and another framework which I explained a bit about (the framework is called JADE)

I: Could you explain another project that is in line with our project ?

M: Told about how I worked with a lecturer over her PhD thesis. (Not a project, but had some work that I thought was in line with their interests)

I: Ok. Are you familiar with concepts in operating systems and computer networks ?

M: Yes Sir, but I’m a bit more inclined towards Algorithms and Data Structures sir (I was better at algorithms and was hoping they changed their mind).

I: I’ll give you a small overview of what we’re working on (told). That’s why we’ll be focusing more on operating systems and computer networks

(...damn it...)

M: Sure sir. I’ll give it my best Sir.

I: Explain about Internet protocol suit (TCP/IP protocol stack)

M: Explained

I: Good, you gave a detailed explanation. Could you explain about Proxy servers ?

M: Explained with a diagram I drew and showed it through the webcam.

I: Ok, consider the same diagram you drew and take one system, the proxy server and a server you want to download from. How many TCP connections and how many HTTP connections will be created between the system, the proxy and the server you want to download from ?

M: Explained my thoughts on how and why should there be 2 TCP and 2 HTTP connections (1 TCP and 1 HTTP between system and proxy, 1 TCP and 1 HTTP between proxy and server)

I: Ok, That is right. good, you were able to reason and come to a conclusion.

I: I guess that’s all the questions from my side. Do you have any questions ?

M: Yes sir, I have one question about the attendance system (SAFE) sir.

I: Yes tell me

M: I saw the brief video presentation about SAFE and found that it can avoid attendance proxies from those not in the class even though it works on WiFi. How does that work ?

I: (Smiled) What do you think ? How does it work ?

M: Explained my thoughts on it and how it could work

I: Ok, you’re close but no it does not work like that. (Eh, well. I at least gave it a shot) He then explained how it worked.

(A bit more discussion on the attendance system and I also put forward my thoughts on my prototype of the attendance system)

I: Did you field test the Bluetooth attendance system ?

M: Yes sir, with 2 classes next to each (Note: I told the interviewer before that the attendance system was a prototype and not a full fledged model)

I: Ok. Just out of curiosity, what were your 1st two preferences ?

M: told

I: Ok, anymore questions ?

M: No sir, that was about it sir

I: Ok.

(End of interview call)

My thoughts:

This is the first ever interview I faced (since I did not sit for placements) and it lasted for 45 mins. The interviewers ensure that we remain calm and are very humble. In my perspective, I found it best to be myself and explain everything that I had known about whatever question they asked. If I did not know something, I would mention that I did not know but I still tried to somehow find an answer that made sense. I would talk out loud and let the interviewer know what I’m thinking. The interview really gave me a new found respect for the professors at IITB.

If whatever I have said so far is more ‘rookie’ for folks who have experienced more interviews, I apologize.

The main point at the end of the interview that I was happy with was that I was able to give it my best at that time, irrespective of whether I’m offered a position or not. What I can truly say about giving interviews now is to always give an interview when provided the opportunity. It’s exciting, it could go sour, who knows ! but at the end of it you will also gain insight on how to improve yourself.

Hope this helps somebody who may have to face an interview from IITB later on. Peace !

Update (7^th July 2020): I have been offered a seat at IITB Mtech RA. I guess the interview went well.  

Interviewer  :--- Hi , Introduce yourself.

Introduced name , GS-698, cat-EWS, Btech in biotech From NIT Durgapur

There was silence for 30 secs after I told biotech

Int:--

Why MTech?

Me:- want to work with computer vision in future and primarily i want a cs degree to be eligible for jobs

Int:- subjects u want us to ask from?

Me:-- LA & prob, OS, DS

Int 1:--  have u heard of linear regression? (me → yes) then tell me if y=A theta ;  then theta = A^-1  *  y ? Am i right?

Me :-- confused with few terms he used in terms of linear regression(like feature vectors and all ). I said as per linear algebra yes

He:- always? 

me:- no, if A is non singular then possible, 

he:--- if that's a non square matrix?

me:-- no still not possible

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He went somewhere, interviewer 2 comes, “ it seems u are having difficulties I will go for very basic questions.”

Int 2:--  A min heap is there .. TC read to get the max element ..

Me:-- O(n)

He:- how?

Me:-- max element is present at the lowermost layer… so we can traverse the min heap using in/pre/post order and just get the maximum

---------------------------------------------------------------------------------------------------------------------

He:-  how to write a program for returning 1 if it has     A[i]= i   or else -1     , if the array nos, are DISTINCT Integers and sorted

me: – traverse it and check the condition

He:--- TC ??

Me:-- O(n)

He :--- optimize it    (Sorry sir,dont know, after thinking a few moments [i missed the word ‘sorted’ in tension])

------------------------------------------------------------------------------------------------------

He:- Prove that for a graph at least 2 vertexes will have same degree.

Me:- Told

he:- ok

----------------------------------------------------------------------------------------------------------

He:-- prove that a DAG has at least one node of indegree 0

Me:- tried but can't do

-----------------------------------------------------------------------------------------------------------

He :--  there is an array with n elements of which k are distinct. Sort them and prove that there TC for this prog is n log k

Me :---- tried but can't do , said sorry sir 

Ok lets try OS as u said,

Me :-- ok Sir

He:-- page size if made smaller what's the advantage and disadvantage

Me:-

the advantage is in an average there is a wastage of page size /2   so if lesser the page size lesser is the wastage

he:- ok and disadv?

me:- disadvantage is lesser the size for occurrence of page fault and thrashing.

he:-- all that's fine, but  i am looking for some other points

me— blank

he :-- it has some effects on page table?

me :-- yes sir the page table size will  increase

he :-- hows that a disadvantage

me:-- sir Page table is an extra burden to the MAIN MEMORY hence , increasing its size is increasing the burden.

he:--- ok, i am done , ask if u have any questions

me:-- no questions, thanks for making me eligible to for the interview

he:-- don't worry, being from biotech, u were good...thanks

me:-- thank u

So this was the scene, it didn't go up to the mark, lets see.

Whatever be the result i am pleased with their patience and gesture of the profs , they were very good and tried to pacify me as much they could

The process of selection for interview at BARC is first we have to qualify the written test conducted by BARC or we can also qualify by GATE score released by BARC. I qualified BARC written test as my GATE score was not that good. Total 98 students were selected for interview for Computer Science and I was one of them.

BARC TS Online Examination Score Cutoff :160.00(This varies every year).( My score was 183.60.The gate score cutoff was 880).

Although, I heard that in 2018 it was 130 (BARC TS Online Examination Score Cutoff ).100 students were called for interview, out of that, 8 students were finally selected for this program ( 700/1000 was my Interview Score where as Interview cut-off was 650).

After that we were given choices to select interview slot. I chose the one on 12th June in afternoon session. I reached BARC centre on 11th June and requested for the guest house which I got (During the interview, the weather ,the view of Anushakti Nagar was awesome, I was flattered (as I am from UP :):). On 12th June we had to reach the interview venue which was next to the guest house. So, I reached the auditorium 5 min before and got my documents verified, and then I was informed that my queue number is 9 and would have to wait for my chance.

My interview started at 03:12 pm and went on till 04:13 pm.

When I entered the room, there were 7 interviewers sitting along a semicircle.

I will denote the interviewers as I1,I2,I3,..,I7  from my left to the right in clockwise direction.

I greeted all of them and they offered me to sit. Then I4 asked me that you don't have your marksheet of 3rd and 4th year why?

I explained (They laughed, I don't know why?).

Then directly I4 asked me to write some 4-5 subjects I'm confident in, on the blank sheets. I wrote Compiler, Data Structure and C Programming, Algorithms, Operating System. Then they said that they were OK  with these subjects.

He asked I7 to start with Compiler. The interviewer didn't ask me direct questions. He started confusing me right from the beginning.

I will try to explain what he actually wanted to ask instead of confusing you all.

Compiler:

How to make a tree for any given expression(working of syntax analyzer)?

In how many ways can we represent an intermediate code, explain with an example?

During the construction of DAG how do we manage to maintain the partially made DAG to check repetition. (Which data structure do we use and how do we maintain it) I was very confused as they were adding there conditions as i replied anything.

What is a hash table how does it works?

Given a language write regular expression, make dfa, and what is the main difference between its dfa and nfa.?

Why do we make nfa, if dfa is easy to make?

How do we use dfa to maintain lexical analyzer( how does lexical analyzer use dfa to track lexemes)

Then I4 interviewer told I1 to move to OS part.

OS:

What is the difference between various types of operating system?

What is the difference between hard real and soft real type of operating system? Why do we use the term hard real time and soft real time operating system.?and it's application.

What is virtual memory?

Given a scenario to design your own operating system which features do you think is necessary for your operating system and why?

(And many more confusing ques not direct so I didn't recall much).

Then I4 told I5 to move to Algorithms.

DSA:

How and why does merge sort works?.

What is the difference between various sorting algorithms and why should we prefer one over the other explain for each sorting algorithm.

Write recurrence relation for merge sort and solve it.

Write a code snippet to delete a given binary tree completely.

Write a code snippet to check two binary trees are same or not.

After this I4 interviewer himself started with C programming.

C Programming:

Can we pass parameter to main function?

How does command line argument works? He told me write code to explain in detail.

Why do we put address in the scanf function? And why not in printf?

What is call by value and call by reference?

After all of this, the I4 interviewer told me that the interview is done and i can leave. It was a one hour long interview but i think they were in hurry as i was the last person for this panel of interview.

I tried to remember as much as possible but there were some more questions.

There were situations that i was trying to explain they said that if i don't know then its OK but i keep on requesting to let me explain they use to laugh and give me time.

I was feeling very proud to be interviewed by these panel and even for reaching there to get interviewed.

And on 27th June, the result was out. There were 8 students who were selected and I was one of them. :)

Feel free to ask your queries.

“Structured, conceptual and practical test of subjects.”

Hi,

I am one of the eight fortunate ones who were selected for OCES Computer Science program last year. I am Abhilash Bhardwaj, currently working as Trainee Scientific Officer in BARC, Mumbai. Last year I was shortlisted for interview based on my performance in BARC TS Online Exam ( 170/300 while cut-off was 159) . Approximately 100 students were called last year for interview, out of that, 8 students were finally selected for this program ( 765/1000 Interview Score where Interview cut-off was 650).

So now coming to interview experience.

My interview was scheduled on 11th June last year. I reported in the morning. After basic document formalities I went to the waiting room. I was second in sequence so nearly after one hour my name was called by the panel. We all have fear of interview especially when you know this is going to last for an hour or so. I entered into the interview room. A total 6 people were there in the room. They started with the basic introduction about my college, my cgpa ( they asked how you managed in college ), my native place etc, just to make me comfortable with the panel.

And here it begins !!!!!

The first question was by the President regarding the subjects that interests me more.They did not ask me to list it down but I jotted it down on a paper. I wrote Operating System, RDBMS, COA , DS and C. Just when I finished,the panel asked that why you have written COA, as most of people don’t write this. ( Don’t answer like its my favourite subject and all, you need to justify it ). I answered the relevance of advancement of architecture, processor design, multiprocessor systems, GPUs in current era. I gave examples of Blockchain and Machine learning where we require high computing power. Then, as I mentioned, I used the term GPU so they began with that… ( so the moral of the story-don’t use just fancy terms if don’t know it!!). Fortunately I was aware of basics of GPU. They asked whether is SIMD,MISD,MIMD or SISD, why we are using this,how it makes computation faster,can’t we achieve the same with CPU, power requirements of CPU and GPU etc. I was knowing the plot not the entire story so at last I surrendered on a comparative question of CPU and GPU, I accepted my defeat. They responded don’t worry it was out of context because of your interest in GPU we asked this much. Then they asked basics of RISC, CISC,current RISC architectures, difference of RISC and CISC, Microprogramming and its types ,Pipelining hazards, how we avoid them, Linking and Loading operations,Addressing modes, CPU flag register etc.

Here my suggestion is to speak relevant to the topic but take examples, explain on paper sheets, draw diagrams. Like when you are explaining Microprogramming start with why we need this, then its categorization, difference etc. They will ask question in every step of explanation. You need to know why RISC, What is RISC and How it is implemented. These concepts are not beyond our understanding. If you don’t know the answer better to say sorry!

Then they switched to Operating system. They started with what was taught in B.Tech. Then they asked me write a critical section program where I was needed to produce H2OH2O. But with different constraints. I used mutexes, again they they asked why mutexes not semaphores ? what advantage you will get by using mutexes? After producing H2OH2O in three different constrained way they asked me a basic question, lets say CPU generated a virtual address, now you tell us complete steps to get the data (structured, conceptual, practical question ) . It looks simple but while answering the question they asked about TLB and its use, memory heirarchy, then different types of cache memories, physically addressed and virutally addressed cache, how page translation is done, what happens if page fault occurs, why interrupt is used when page fault occurs, concept of virtual memory and its use etc. I explained all steps with diagram by taking examples. Then they asked about thrashing, Page replacement and Belady’s anomaly, example where FIFO algorithms shows Belady’s anomaly.

Then they asked a bit more about virtual memory.

After OS they shifted to RDBMS, they started with why we require normalization and what all concepts you learnt in B.Tech. Then they asked me to write a nested SQL query to fetch some data ( I remember it was lengthy ). Then they asked about locking mechanism in database, how locks are implemented in any database, what data structures are to be used to implement locks and some questions related to transactions.

Next they started with C. Process image in RAM when program is loaded ,basics of all four segments and what they contain ,what is an extern variable and its use,storage class of global variables,how to define structures in C ,represent a rectangle using structures in 2D coordinate system then using this structure to write a program in C to check whether two rectangles are overlapping or not .I defined rectangle initially four points but they asked to improve it, further I changed it to origin points, length and breadth. Then I wrote the function to check the overlapping.

Overall, interview was pretty nice.I answered most of the questions. There were very few places where I was stuck and wherever I was unaware of the exact answer I said sorry. Like they asked me about convex hull and I was not much sure about that so straight forward I said sorry.

My basic strategy was to stay calm, listen to the question carefully and to think before answering even if the question may seem very easy. I used the given paper sheets to draw diagrams, write examples. Whenever it was needed I explained the things by showing steps and sequence on paper. I related my learnt concepts with real life as well as other subjects, like COA with OS, Transactions with shared memory access etc. Throughout the Interview the panel will help you .When you get stuck they will try to point in correct direction so that you can rectify yourself.

Thank you for your utmost patience to give it a read.I hope this small piece of my experience will be of some help to the aspirants. All the best !!

I will be posting some other contents related to BARC. Feel free to reach me in case any doubts:

https://www.linkedin.com/in/abhilash-bhardwaj-6000b7b4/

www.facebook.com/abhilashbhardwaj.kasap

If you are looking for Masters in research then this is not a good place for you.but if your main concern is Placement then this is the place for you.

 M.Tech (2018-2020)  students placed in companies are as-

Qualcomm, Sandisk, Samsung R&D Noida, Royal Bank of Scotland, IBM, Mobikwik, Policy bazaar, Dunnhumby, Schlumberger, Nagarro, Amdocs, Tejas networks, Axteria , Shipsy, Intello labs,  Yodlee envestnet, Smart energy water, American Express, etc.

Academics wise, this is not that much good but when it comes to coding culture it is above average and campus life is just awesome simply, after every 5-10 days DJ party is here. Fests like Yuvaan & Engifest is very popular and you will get too much free time for any exam or placement preparation.

This year highest placement is 29 lakh in Qualcomm for 3 students following by 20 lakh in Sandisk for 2 students  and so on… Still, placement is in process for the current batch (more than 80% are placed with the average package of above 14).

Each year more than 300 companies visit here for B.tech in which 150+ are open for Mtech (CSE+SWE+ISY). All three specialization get equal opportunity. (if you are good in coding with good communication skill then you have many opportunities otherwise you can try for the different profile like data scientist, analyst etc ) which also offer above 10 LPA.

M.tech is allowed in companies like Goldman sachs, Uber, Microsoft, flipkart, Amazon and many more but they take very hard coding test so it is very hard to crack due to high competition.

For coding practice we usually follow GFG, hackerrank, codechef, etc.

For admission DTU consider only GATE score (total of 20+20+20 seats are in each specialization(CSE+SWE+ISY)):-

 for General Category in round 1 under 1000 for CSE and till 1700-1800 is safe for SWE with 2000 for ISY.  Sometimes magic happens in spot round like 4000-5000 gate ranks can also get a seat( which usually does not happen and goes till 3000).

NOTE :- Computer science(CSE) and software engineering(SWE) comes under Computer Science department and (ISY) in Information technology Department.

All get equal opportunity in placement but usually, students take CSE then SWE then ISY.

If your goal is to become teacher or to get PSU then again you can think of DTU as colleges like KIET, DIT University and Bharat Electronics Limited(BEL)  and many more come each year.

For any further query consult any placed M.tech final year student they will definitely guide you.