Recent posts in Interview Experience

This year IISc had record number of applicants for CDS Department. So they had divided the screening process into 4 days, each day having 2 shifts.

The screening process had a written test(Different tests, based on if you choose CD-CS or CD-CP), succeeding in which, was followed by an interview. The written test had 5 simple questions to be solved in 30 minutes. Questions were almost as easy as the GATE 2019 paper.

They called me on 20th May, morning shift, 9am, so naturally I reported at around 8am. The exam started at 9.10am’ish time, went upto 9.40am. Soon after the exam got over, I asked Yogesh sir, if we could quickly check the canteen, as I was hungry as hell. I was told that results will be declared at 10am sharp, and I should decide if I would be on time. Prakruti, the canteen, had a huge queue at the token counter, so alas, I stayed hungry.

Shortlist was out. My name was called, was asked to report at room 201. Waited for quite sometime outside, listening to “Hall of Fame”, by the Script, on loop, on my headphone. and then came my turn. I was called in, and asked to take a seat.

(I DONT REMEMBER WHICH QUESTIONS WERE ASKED BY WHOM, SO I WOULD USE “I” IN GENERAL FOR INTERVIEWER)

I: So Mriganka Shekhar Chakravarty is your name. And you have a Gate score of 729, with an AIR of 558. Am I correct?

Me: Yes, sir.

I: I see you have chosen CD-CS with Cloud Computing as your first choice for lab. Is it correct?

Me:Yes Sir.

I: But, Mriganka, in the online form where you were supposed to make choices, you selected CD-CP as your preference and now you have switched to CD-CS? Why so?

Me: I dont remember sir, however, that indeed might be a mistake on my part.

I: Okay. No issues. So tell me Mriganka, what are your strengthened subjects?

Me: I feel comfortable with Algorithms and Data Structure.

I: But you have chosen Cloud Computing as your lab right?

Me: Yes sir. But I believe, Algorithms is a subject, which if strengthened can be a launchpad for any other stream of specialization.

I(Everyone smiles): True that, but knowing algorithms is a “Necessary condition, not a sufficient condition”.

Me: I agree sir.

I: Okay, Mriganka please stand in-front of the board, and draw a grid structure.

(TRUST ME, THE WHITE BOARD WAS HEAVEN….. IF YOU EVER INTERVIEW AT ROOM 201, YOU WILL KNOW IT)

I: So Mriganka, you are standing at (x,y) on the grid, and you wish to go to (p,q). What is your shortest path?

Me: Sir, if you could kindly stress on the constraints. Am I allowed to take diagonals on the grid?

I: Yes, you can take right, down and diagonals.

Me: Explained my approach. I started scribbling the mathematical model of the situation.All the while, I kept speaking of what I am thinking. After, sometimes, I came up with the equation that gives the shortest path, dependent on x,y,p,q.

I: Can you prove it?

Me: I started the proof. Stumbled. kept scribbling. I failed. I however remember saying, “For this to be shortest, we need to show, that (x,y) to (p,q) cant be reached any any number of steps shorter than this, basically we need a contradiction approach”.

I: Okay fine. No problem.

I: So do you know what a diameter of a graph is? It is the longest of the shortest paths within the graph. So given a graph, can you work out the length of diameter of a graph?

Me(Holy F**k inside…premature optimization is root of all problems, take it easy and brute force :P): Sure sir. So it is a shortest path problem. Let us run Dijkistra’s on all the vertices, and from among them choose the maximum. This is easy.

I: Okay…. So what is the complexity?

Me: It is O(VElogV) for dijkistra run V times. and O(N^2) for choosing the maximum of the shortest paths. So the complexity is O(EVlogV)+O(V^2).

I:Can you optimize it further?

Me(Quiet for a few moment): I can only worsen it with Floyyd Warshal, with a smile!

(He was probably looking for Johnson’s Algorithm)

I: Okay, Mriganka draw a binary tree.

Me: Drew.

I: Count the number of children, and the number of nodes with two children. and name them N0 and N2.

Me: Did.

I: Now you can see, that N0=1+N2. Prove it.

Me(I WONT USE INDUCTION): Started working around with the degree equations. Got tired after sometimes(I AM HUNGRY). Sorry sir, it would be helpful you could give me a direction to work around(with a smile).

I: Use Induction.

Me( :( ) : Did that.

I: Okay Mriganka, take a seat.

(I DID NOT NOTICE, BY THIS TIME THEY HAD BISCUITS AND SNACKS ON THE TABLE, AND I WAS HUNGGGGRY)

I(No they did not ask me to take snacks xD): Asked a few questions from operating systems, on process isolation and stuffs.

Me: Answered, but I am not personally satisfied with the OS interview. I could do better.

I: Okay, Mriganka, you may leave now :)

Me: Thank you sir :)

I: You must be really hungry. Have some food. You were the one asking to check the canteen out right?

Me: Yes sir, I am reaaaly hungry. Had nothing since morning.

I: See you.

24th May…………….CONGRATULATORY MAIL :)

I got selected in IIT Kanpur, and this is the reason why I started preparation for GATE in the first place, so for me, this is pretty much the same as getting AIR-1 in GATE, This was made possible only because of my brothers, whole GO community and specially Astitva[It feels like for 2 years we’re only discussing questions and concepts together]

About me: https://jun03.github.io/portfolio/

GATE 2019: marks- 63.33, Rank – 582[In 2018 at marks 63.33 rank was 176, you can imagine what will happen in 2020]
IIT M: Did not qualify the written test

IIT K: Selected in MS

Cleared written of BARC(Preparing for Interview).

Post GATE :  

Did all coding assignments(Special thanks to Digvijay sir), participated in codechef competitions, got back on Hackerrank, Completely read OS:3 easy pieces with its homework assignments, revised GATE concepts, I used to collect questions and take Astitva’s interview and he did same for me (It was really helpful)

Written Test: Logical questions mostly which check your understanding, ex: Program whose output is based on endianness of system, order of socket primitives, etc.

Programming - 3 Questions[Main program(40 points) was to complete function to input and merge two sorted linked list], All were easy- finished them in 1 hour while given time was 2 hours

Interview: My interview was comparatively shorter than others 10-15 minutes
They asked me to take a seat, then sir said: So you're a system guy, huh? I said yes[I don't know why but a cool dude voice in my head said: Yeah, I'm a system guy, It kinda felt nice to hear something like this], then they asked about my college, I mentioned name - they asked me twice to confirm because maybe they hadn't heard of such a college name before, they asked me about programming test, I said I completed those before time and passed both hidden and visible test cases,then a couple of general question then it started:
P- professor, A - me
P: Asked for preferred subject
A: Operating System
P: What are the major projects you have done in OS, or what work you have done related to OS
A: I haven't done any major projects in OS, but I have made programs to emulate various activities of O.S. like scheduling algorithms, calculating cache misses, calculating various cache sizes, etc.
P: In which language you wrote these emulators
A: I said mostly C but have used python for some complex ones.
P: Why have you used Python
A: Because it's relatively easier to write a program in Python than in C.
Then a few general questions about Python like why it is slow etc, I answered correctly.
NOW COMES THE MAJOR QUESTION
P: Suppose you have an already compiled program as an object file and you have to run it in this laptop and what I did is that I removed OS from it, will you be able to run it?
A: No sir[I was thinking correctly like running such a program would require O.S. support but got tricked in his next statement]
P: OS is also a program right, written in C and Assembly, How does it run?
A: Explained about the bootloader.
Some discussion on how bootloader will run, what is firmware code[I'm not describing it much because it went quickly and I don't remember exactly]
P: So coming back to the original question- we can run this program without OS rt?
A: Yes sir, we just need to place it in the disk at the location where O.S. normally reside and it will run
P: But this program is compiled in an environment with OS, i.e, Virtual memory and for address translation and some other stuff it'll need OS, right?
A: Yes sir, It'll not be able to run without OS support.
P: What will happen exactly- tell me that
A: It'll try to access virtual address which can be invalid.
P: What will happen exactly when it'll try to do so?
A: A trap would be generated[I wasn't sure so I kinda said in a low tone]
P: What?
A: Sir the Hardware will generate a trap
P: Okay, He asked with other Professor if he wanted to ask, but they agreed that it's ok, and they asked me to leave.

At that time I wasn't sure whether it was a good interview or bad[I still don't], but the only thought in my head was - What about threading, implementation of scheduling algorithms etc- the stuff I read so much about, why didn't they asked anything on that, but that's the thing these Interviews don't need you to do/know a lot- just make sure you really understand what you know and be smart[like adaptable to different situations]

Pro tip: Decide your subjects(At least 2) from now and for that, you need to decide which type of work you want to do, It'll help you a lot if you have done some work related to this subject/field. At least I would say for these two subjects you should study proofs[If theory based] or Implementation code and some tools[System side]. If you want to be in AI/ML, among other things, prepare Maths definitely and don't just practice blindly- try to get an understanding of things like what is matrix multiplication, what is the reason for calculating things like Eigenvalues, Eigen-vectors, etc. Do visit the IITs CS department website

Question 1: (8 marks)

Write a program to print the pattern below. Taking n as input, print n lines that print the pattern.

Sample input 1:
3

Sample output 1:
*    *
**  **
******

Sample input 2:
5

Sample output 2:
*        *
**      **
***    ***
****  ****
**********

Question 2: (12 marks)

The int datatype has a limitation of maximum value. It can only store values upto a certain limit. So what we want to do is take a very big integer and add 1 to it.

INPUT FORMAT:

First line contains number of digits in the integer, n. This is at maximum 50.

The next line consists of all the digits of the integer, separated by spaces.

You are required to add 1 to this integer and output the digits of the resulting integer (without spaces)

Sample input:
12
8 7 5 1 2 5 4 8 7 5 4 5

Sample output:
875125487546

Question 3: (8 marks)

Leap years are an interesting way of putting together lost time over the previous 4 years. These are those years when February has 29 days. One of your friends Raj was born on 29th of February. He wishes to know how many times till date he lived through his actual birthday (29th February). Take his birth year and present year as inputs and print the number of times he has experienced 29th of February. Note if present year is a leap year, do include its 29th of February as well. You may also display an error as “Birth Year is incorrect” if the birth year entered is not a leap year.

Note: Leap years are years which are multiples of 4 with the exception of years which are divisble by 100 but not by 400.

Sample input 1:
1996 2019

Sample output 1:
6

Sample input 2:
1997 2019

Sample output 2:
Birth year is incorrect

Question 4: (12 marks)

Sort an array in ascending order by flipping (exchanging) 2 adjacent integers not in the correct order until there is no such pair.

The leftmost swappable pair must be swapped first, i.e. the first pair encountered while going from left to right, which is in the opposite (descending order) should be swapped. Then the whole process should be repeated.

INPUT FORMAT:

First line contains 1 integer N denoting the number of integers in input. Next line contains N integers separated by spaces.

OUTPUT FORMAT:

For each flip performed, display the array in a line separated by spaces.

Sample input:
5
10 7 6 2 5

Sample output
10 7 6 2 5
7 10 6 2 5
7 6 10 2 5
6 7 10 2 5
6 7 2 10 5
6 2 7 10 5
2 6 7 10 5
2 6 7 5 10
2 6 5 7 10
2 5 6 7 10

Question 5: (12 marks)

In this question we’ll deal with Fibonacci series. The series is defined on whole numbers like fib(0), fib(1),… as follows:

fib(0) = 0

fib(1) = 1

fib(n) = fib(n-1) + fib(n-2), for n >= 2

INPUT FORMAT:

An integer N, 0 <= N <= 1000

OUTPUT FORMAT:

Add the unit digits of all the Fibonacci numbers from fib(0) to fib(N) and print only this sum

Sample Input:
8

Sample Output:
24

Question 6: (8 marks)

You are to write a program which takes 2 complex numbers as input and prints the sum and multiplication of the 2 complex numbers.

INPUT FORMAT:

The first and second lines contain 2 integers (the real and imaginary parts) for each complex number involved.

OUTPUT FORMAT:

The complex numbers sum and product on separate lines in the form a+bi or a-bi (depending on whether the complex part is negative or not).

Sample input:
1 2
1 3

Sample output:
2+5i
-5+5i

IITM-2018

IITM-2016

IITK-2018

IITK-2018

IITK-2017

IITK-2016

IITK-2016

IIITH-2018

IIITH-2018

IIITH-2018

IIITH-2017

IITD-2018

IITD-2018

IITD-2018

IITD-2017

IITD-2017

IITH-RA-2019

IITH-RA-2019

IITH-RA-2019

IITH-RA-2018

IITH-TA-2018

IITH-RA-2017

IITH-TA-2017

IITB-RA-2017

IITB-RA-2017

IITB-RA-2017

IISc CD-CS-2018

IISc RA-2018

IISc-CD-CS-2017

IISc-CD-CS-2016

250 students got interview call for the 2nd round, out of which finally 7 got selected for this program.
Shortlisting criteria

3 rounds were taken- Aptitude test(about 23 got shortlisted, about 100 showed up), 1st Interview(13 got shortlisted) and in final interview 7 got offers.

1. Aptitude was an easier version of gate(only technical aptitude).

2. Two professors were there, who asked me for my CV(seldom it happens). They asked for my introduction and I think they were a bit impressed with that.
They asked what I did in 2017, after passing out and various general questions like why I didn't attempt Gate in 2017, did I take any coaching, etc.
After that, they asked me an algorithm question and told me to explain my logic on board. They asked me to calculate the time complexity of the solution I suggested. They looked a bit satisfied.

They then moved to Networks and asked lots of questions. The questions were a little bit practical rather than theories we have gone through while Gate preparation. Since I was not really good with that, I tried to explain whatever I knew and admitted that I don't have that much of practical knowledge(I would advice to not directly jump on to this "I don't know" thing).

They asked me questions related to OS like multithreading, multiprogramming, implementation of multithreading with socket programming, practical examples of where these techniques are used.
They also asked me to rate myself in coding out of 10 and about what was the biggest/challenging code I have ever written.

My interview lasted about 15-20 minutes and was not expecting to get shortlisted.
Results came and then here starts last round.

3. Three professors gave a small introduction to projects they were having vacancies in. We were supposed to enter our preferences.
Then the interview started and they asked me different questions related to core subjects the projects were in like- Networks, Compiler, and Computer Architecture.
I was asked if I have any other calls and I told them about IIITA. Since the offer acceptance date of IIITA and interview date of IITH were clashing, I took a risk.
(non-refundable 40K were already paid in NSR round, that is another part).
They asked me various HR type questions like about my preferences, etc. And they looked quite happy with my answers. (This time I didn't have any gut feeling of rejection).

Just the next day, results got announced and finally, 7 people got offers and efforts finally paid off!

Since I have gone through a long journey, before this little success, I have some suggestions for those who are willing to get through.
Ps. Toppers' suggestions can help you better to score exceptional, mine can just add on to them so that journey becomes worth remembering.

My suggestions would be:
1. Not to quit in between. Here I am talking about starting with full enthusiasm and planning to reattempt even before attempting.

2. No matter what comes to your way, don't ever lose your hope. Keep faith even when everybody loses it.

3. There is no substitute for hard work.

4. Hope in every opportunity that comes to your way, maybe that is where you belong.

I will try writing a blog on GO/ Quora about this journey, where an average scorer landed up in the best.
I wish you all the luck. Thanks for reading

GATE Score: 604

Rank: 1644

Category: GEN

There was a written test followed by the interviews. Only the candidates who cleared the written were eligible for the interviews. Around 50 students appeared for the written test on 26th November.

Written Test:

The difficulty of the test was comparable to that of the GATE exam (although there were some extra topics). There were questions from Algorithms, Programming, Compiler Design, Probability, Linear Algebra and also some (around 5) questions from Machine Learning. There were 20 total questions. A blank paper sheet was also provided for doing rough work.

(Trying my best to recollect the questions)

1. Algorithms Question => Related to the worst case and the average case of the Quicksort algorithm. (There were some cases and the correct option was to be selected)
    
2. Evaluate a prefix expression.
    
3. A question from compiler design => What is a+++b? 
    
4. Machine Learning Question => What will happen if we increase “k” in K-means clustering? (I don’t remember the exact options but they were related to variance and bias. I was able to answer.) 
    
5. Machine Learning Question based on Classification => Minimum number of one-vs-one classifiers required to classify 6 classes? (Multiple options.  Answer: 15)
    
6. Machine Learning Question => Which ML algorithm will be used to predict the number of calls in a call center based on previous data? (Multiple options. Answer: Linear Regression)
    
7. A question related to parallelization of 2 code segments. Two loops were given where we had to tell which of those 2 can be parallelized.
    
8. Some questions on probability.
    
9. A couple of questions on linear algebra.

(Sorry! That’s all I remember)

I answered around 15 questions and got shortlisted for the interview round. 20 candidates were selected for the interview rounds.

The Subjective test:

This test was only meant for the interviews. It was not to be used as a shortlisting criterion for the interviews. There were 2 questions, one on designing an algorithm and other related to distributions in probability.

I was only able to answer the algorithm question. The question is as follows:

Question:

A person is stuck on a square island which can be represented using an NxN matrix M. The person is allowed to take n steps. In a single step the person can move in either direction. The person dies if he steps out of the island. Give an algorithm to compute the probability that the person will stay alive after taking n steps.

The Interview:

My first interview panel had 2 professors.

Interviewer 1 (from Compilers background): Tell us about yourself.

Me: Told about myself. About projects I have done in the past, my research interests, etc.

Interviewer 1: Okay! So you have answered the question related to parallelization (in the written test, it was the correct answer). * He stood up and wrote those 2 code segments on the board *. Can you explain?

Me: I explained why one code segment can be parallelized and why the other one cannot be parallelized.

Interviewer 1: What is the order of parallelization in terms of big-oh?

Me: O(N). It was a for loop running N times. Each run was independent,

 * Some more discussion on why the other one cannot be parallelized *

Interviewer 1: * wrote another question from the written test and asked me to explain *. The question was the evaluation of a+++b.

Me: I told him how it will work. Gave him Finite State Machines for it. He was quite impressed.

Interviewer 1: Okay! What about a++++b?

Me: Explained.

Interviewer 1: And what about a+++++b?

Me:  * At this point, I was like, what?* I tried to explain as much as I could. He was satisfied.

Interviewer 1: He then gave me some languages and asked which machines (FA, PDA or TM) can accept them?

Me: answered.

Interviewer 1: Asked about my BE project and what algorithms I used in it.

Me: I answered.

Interviewer 1: Okay! We are done.

Interviewer 2 (from Computer Architecture background): * Finally broke his silence * Are you interested in answering CSO questions.

Me: I told him that I’m not good with that subject.

Result:

Selected. I received the offer letter on 20th December.