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Hello Everyone. I am Neelam Singh passed out in Aug 2021   from a private Engineering college in M.P Bhopal. I appeared for BARC written test in CSE on 25 Sept 2021 and interview on 11 Nov 2021 and by god grace ,I cleared the interview in  first attempt.

How I prepared?

I took guidance from Deepak Sir and Sachin Sir from GO classes. GO Classes helps me to clear my concepts and build my career . All the teachers explain in very detailed and nice manner and also have doubts classes at the end of every class. Sachin Sir and Deepak Sir are highly supporting ,knowledgeable and friendly. I will suggest every GATE and PSU aspirants to go through the free course of DM and C on GO Classes.You will love it .

For written test , I went through the notes of GO Classes and Applied Gate .For interview I refered GO classes notes(for C, DS,Algo) , Geeksforgeeks articles(for C,DS, Algo, DBMS) and GateBook notes for CN .

What all subjects I chose for Interview?

I chose C, DS, Algo , DBMS ,CN . But they also asked OS . They consider one programming language and OS as almost  neccessary  .

what all questions they asked ?

C

1.Write C program to merge two sorted arrays into one and return new sorted array.

2.Why you prefer C over other languages ?

3.Where global and static variables are stored ?

4.How will you return an array build inside a function? (Hint:- using malloc )

DS

1.State some uses of stack DS?

2.How System Stack works?

3.What all activation record contains?

4.What DS will you use to store variable length URL?

5.Write node structure for stack used for storing forward and backward links/URLs visited , while browsing?

6.How stack helps in storing /performing undo or redo operations on the URL visited?( Hint:- By maintaining 2 stacks )

7.Write code for push and pop in stack implemented using Linked List?

OS

1.What is OS?

2.What are all functionalities of OS?

3.What is process?

4.Draw process state diagram?

5.What happens when process is in new and end state in process state diagram?

6.What all resources are allocated to a process?

7.What PCB contains?

8.How PCB is implemented?

9.What is process synchronization?

10.How process synchronization is achieved ?

11.What is semaphore?

12.Write code for synchronization using semaphore?

13.How can 2 processes access same semaphore variable?

14.If suppose a process generate address corresponding to other process memory space , will it be allowed to access? If yes , How? if no, How?

15.What kind of addresses a process generate ?(Virtual or physical)

16.How much memory , a process think it have and it actual have and how mapping is done between two? (concept of virtual memory and pagetable ).

17.What is swap space?

CN

1.Explain how a process will send data to another process on host on another network ?x

2.How ARP protocol works?

DBMS

1.What is transaction?

2.State properties of transaction?

3.How isolation is achieved in transaction management?

4.What if we allow non-serial schedules?

5.What is normalization and explain its type?

6.Do normalization impact performance . If yes , How?

7.When should normalization be performed and when not?

ALGO

1.Suppose you are given a array, return N subarrays such that their sum (sum of elements of each subarray) difference is minimum . Suppose S1, S2,..Sn are n subarrays sum ,then |S1-S2| +|S1-S3|+….+|S1-Sn|+|S2-S3|+|S2-S4|+…. should be minimum . Give algorithm for it.

2.Give greedy algorithm for above problem?

TIPS:

1.Prepare one programming language and OS .

2.Explain in detailed manner, every question.

3.While preparing look at implementation side of every concept , espically in OS,DS.

4.Don’t mug up the concepts . Try GOClasses once.

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Exam: Jan 2020

Shortlist for the interview: May 2020

now coming to my interview

Interview Experience :

Date of interview-  4th/March /2021

Venue- DOS,Delhi

Interview mode: Zoom call in ISRO center (thanks to covid)

Reporting Time- 8:30 AM.

My interview was started at approx 11:00 am.

After entering the interview hall, I was connected with 5 ISRO centers over ZOOM call(around 15-18 scientists overall)

Transcript notation -> <center> : <message/interaction>

• VSSC : Vikram Sarabhai Space Centre
• URSC : U R Rao Satellite Centre
• SAC : Space Applications Centre
• SDSC : Satish Dhawan Space Centre (He didn’t speak a word, but sir was observing entire interview)
• C1 : no idea which center it was

VSSC : Good morning!

Me : Morning sir.

VSSC : ok tell me the technologies you are comfortable with (no intro no nothing lol, straight to business)

Me: am comfortable with ML and AI and am currently doing masters in the same

VSSC : relation between two (answered)

VSSC : define Data analytics (answered)

VSSC : components of Data analytics ( sorry sir and end)

VSSC:  (looking at my bio-data form) here you have written you have worked on some IoT applications during your time in XYZ org.

Me : yes sir that was an Internship.

VSSC: Internship? we thought it was full-time(since the description was complex)

Me: Yes sir, I was responsible in so and so part of that project.

VSSC: makes sense, tell me your fav programming lang.

Me: am comfortable with C and python.

VSSC: python! very good.

VSSC: does python have arrays? (answered)

VSSC: the difference between list and arrays? (answered)

VSSC: over to you URSC

URSC: what does ‘&’ do in c? (answered)

URSC: ‘&’  can be used in before function and variables right, what’s the difference? (answered)

URSC: what is a union?

URSC: alright, suppose you have an integer array of 40bytes, you need to access it byte by byte, how will you do it? (told type casting approach)

they stressed on this question for few mins, I couldn’t come up with the approach they wanted and they finally said hint was the previous question(union), then I was like ahh. then they directly moved on to the next question, no answer and all.

VSSC: you must be comfortable with CPP also right since you know py and c?

Me: Am rusty in CPP but I can answer few questions. (MISTAKE)

VSSC: what does ‘&’ do in CPP? (ikr ‘&’ day lol)(answered)

VSSC: what’s the difference of ‘&’ in c and cpp(half answer)

VSSC: the difference between public, private and protected (messed up big time here :( )

VSSC: ok (I could feel that disappointment in their face)

VSSC: function aliasing in CPP?(answered but they went deep got stuck)

Here I ACKed that my CPP and OOPs are rusty

VSSC: No problem, it’s natural. (I was like wow)

finally, they asked fav subjects. told OS,COA and TOC

VSSC: Over to you C1

C1: What is zombie process(answered 2 times with example,they were not satisfied)

C1: the difference between file structure and data structure? (not answered properly, then they themselves gave out definitions)

C1: Where is the file structure stored and where is a data structure stored? (again with hint was able to tell)

C1: Types of message passing?(answered standard ones which are in Galvin but, they asked for more)

C1 was not happy with half of my answers, so I felt a bit low since OS was my fav subject.

C1 : we are done

VSSC : over to you SAC

SAC : What is LAN ? (answered)

SAC : How is it different from MAN and WAN? (told: distance and medium, he laughed )

SAC : Ok tell me the difference in the distance then (told but, interchanged MAN and WAN. he again laughed and said MAN is bigger than WAN, then I corrected it)

SAC : (Scrolling through my UG marks cards) define SAN (answered)

SAC : Types of SAN? (forgot)

SAC : What is NAS? (answered in short, he expected more)

SAC : Two simple questions regarding OSI (answered)

SAC : Ok am done (and laughed)

This laugh was messing around in my head. like I was only thinking “did I do that bad during C1? “(form here only downhill)

VSSC : super scalar processor ? (answered)

BIGGEST BLUNDER that led to my results ;-;

VSSC : Throughput of pipeline processor (a simple and basic question(I know) but, messed it up in follow up questions)

since my mind was playing with me I answered it so badly that even I wanted to punch myself in the face.

VSSC : Ok URSC over to you

URSC: what is coupling and cohesion? (answered)

URSC: we do ground testing of rocket software here and you might be aware of generic software testing, how is it different? (answered in a general sense, ma’am was satisfied)

URSC: Have you ever heard a language named as ADA? (I was like what??? then she asked which textbook did you read during advanced computer architecture, this was a subject in BE which I never read. so you know my reaction lol)

URSC: few more generic questions on CPP (I answered 4/6)

URSC: define hypervisor (told about layer but they were seeking actual definition)

URSC: We are done

VSSC: Thank you we are done

well, the interview lasted for 34mins there were ups and a lot of downs(lost focus in between). I knew that I was out but, after hearing few other interview exp from my friends I thought my questions were a bit tricky and had little hope that I might get In.

but in the end, I FAILED in getting into the merit list (not even waitlist, as expected. you can’t mess up a simple COA question) but had a lot of learnings from it.

Learnings :

- Every stuff is important, these experiences are just for reference, they know and ask everything in an interview(It’s like that saying “if you even have a single point of failure then you will fail”).

- Here they focus more on the quantity of topics covered, in-depth helps but, try to read extra stuff for your fav subjects.

- They see your BE marks card so know the basics of few subjects you covered in BE(especially 4th year ones).

- Whatever happens, keep your focus in the interview (else you will end up like me)

- Luck does matter a lot but it can be overridden by hard work along with practice (practice with others as much as possible)

well, this was my story/exp had a lot of fun giving this interview, I mean you see few scientists who come on TV during the launch(fanboy moment).

I have given a lot of private MNC interviews but never felt this happy. so this interview has its own class.

give your best! (One day I will get there, passion > money :P)

and congrats to the guys who made it in, you truly deserve it :)

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Date: 20-07-2020

There are 5 interviewers in panel

Prof1 : (smiling) Devendhar right….?

Me : Yes sir

Prof1:  You from Telangana ?

Me: Yes sir

Prof1:  How are you? and is everything fine ?

Me : Im fine sir, thank you.

Prof1: How is the covid situation in your town?

Me: Now situtation is improving in my town sir and day by day becoming normal.

Prof1: I hope you and your family is safe ?

Me:  yes sir, thank you.

Me: Introduced Myself

Prof2: Programming question

Given a 2d matrix which contains 0's and 1's only, is there any row contains all 1's ?

They gave me a link of notepad and said me to write code in it.

Me :  I wrote

Prof2: Okay, Done with you.

Prof3: Which subject you chose ? (they gave me a link before the interview to choose the primary subject)

Me: OS sir

Prof3: What are the different scheduling algorithms?

Prof3: What is the pre-emptive scheduling algo?

Prof3: Given a problem (AT, BT), find avg TAT, WT using Round robin algo?

Prof3: What means TAT?

Prof3: How to choose appropriate Time quantum ?

Result : Selected

4

Hello Everyone !!!

The written exam happened on 12th Jan 2020 and the shortlist for the interview came on 9th May 2020. I was not much confident about the ISRO examination result but I got shortlisted for the interview.

Interview Experience :

Date of interview-  10th – March -2021

Venue- NRSC Guest House Conference Hall, Balanagar, Hyderabad.

Time- 8:30 AM.

In the big reception hall, everyone was asked to sit and wait for their turn. At appx. 8:30 AM, they verified the documents and covid report. Document verification was done. At 8:45 am they called me inside of another waiting room. I was waiting outside of interview hall.

My interview was started at approx 9:00 am :

As I entered the room there was a big table with big screen, and panel head (PH) was on the screen. then panel head asked me to sit.

PH : (smiling) Devendhar right….?

Me : Yes sir

PH:  You from Hyderabad (Telangana) ?

Me: Yes sir

PH:  How are you? and is everything fine ?

Me : Im fine sir, thank you.

PH: How is the covid situation in your town?

Me: Now situtation is improving in my town sir and day by day becoming normal.

PH: I hope you and your family is safe ?

Me:  yes sir, thank you.

Me: Introduced myself.

PH: Which programming languages you are comfortable?

Me: C, Java

PH: What is OOPs?

PH: What is Polymorphism ?

Me: Answered (but could not defined in proper way)

Then he asked one of the panel members to continue…

P1 :  what are your favourite subjects ?

Me: Data structures, Algorithms, Database and management system, Operating system.

P1: What are the functions of OS?

P1: What are IPC Mechanisms?

Me: Answered (I mentioned only few)

P1: Any other IPC mechanisms  than what you told ?

P1: What are various process states ?

P1: What is pre-emption?

P1: What are synchronization mechanisms ?

I answered all of them, then he moved to C

P1: What is Declaration and Definition of a variable? difference between them ?

P1: What is Postfix and Prefix?

P1: What is Structure and Union? Difference ?

I answered all of them, then he moved to Computer Networks

P1: LAN vs WAN ?

P1: What is Ethernet ?

P1: What is CSMA/CD and explain in detail?

P1: What is firewall and Why we use it?

P1: What is Denial of service attack ?

I answered and all of them, then he moved to Software Engineering

P1: What is SDLC and what are the phases ?

Me: I gave definition, bt he asked me explanation of each phase. Then I explained the each phase.

P1: What is whitebox testing and blackbox testing ?

Me: First, I gave definitions bt bt he asked me to explain. I explained.

Then he asked one of the panel members to continue…

P2:  Are you comfortable with compiler ?

Me: yes ma’am (with doubtful face bcz I didnt mentioned in fav subjects)

P2: Why compiler ?

P2: What are the steps in designing the compiler?

P2: What is interpreter and compiler? differences?

P2: Is compiler platform dependent ?

Me: I said yes

P2: If I compiled one program in one machine and can I run it on another machine or Do I need to compile again?

Me: Yes ma’am, need to compile again

P2: are you sure ?

Me: Yes ma’am

P2: really ??

Me: We can use cross compiler also ma’am.

P2: Ok… I’m done with you.

P3: you did project in Deep learning right ??

Me: Yes, ma’am

P3: What is neural networks ?

P3: What are different types of neural network connections ?

P3: Different types of learning algorithms?

P3: Which one is used in your project ?

P3: What is the benifit of Reinforcement learning ?

P3: What is Activation function ?

P3: How you say it converges and when you stop ?

Me: answered (but could not explain in proper way)

Then the Panel head said that we are done with your interview and asked me to leave.

My interview lasted for around 30 – 35 minutes.

Result : Selected

I would like to wish all the best to ISRO and GATE aspirants.

I would like to thank GATEOVERFLOW specially Arjun Suresh sir, Bikram Ballav sir and all others who are working to guide computer science students.

Thank you

5
ISRO - Dreams do come true

Since 2017 , I have been reading the success stories of many ISRO aspirants of CSE from various source and always had dreamed about writing a success story. I guess the day has finally arrived. Failures have been my constant companion , but it laid the stones to my success finally. Let me give you a brief background about myself.

I am Sandeep Nithyanandan. I am 2016 B.tech graduated from Sreepathy Institute of Management and Technology , a private engineering college in Kerala . I completed my M.tech in Computational Linguistics , from GEC Palakkad in Kerala in 2019. I have been working since then in a
irm.

My Gate and ISRO exam details:
Gate 2016 - not cleared, ISRO 2016 - written not cleared

Gate 2017 - AIR 4497 , ISRO 2017 Dec - Written not cleared

Gate 2018- AIR 3039, ISRO 2018 - Written not cleared

Gate 2019 - AIR 1916, NO ISRO exam in 2019

Gate 2020 - AIR 1445 , ISRO 2020 (it is 2019 notification)- Written 108 marks and Cleared

Gate 2021- AIR 2297.

After seeing my performance you might be thinking is this guy mad. To be honest , I was never a bright student at all, my Gate score tells the same. But one thing which i did was I never gave up (being a Manchester United fan ). I kept on preparing for Gate even during my M.tech time as well as working time. Consistency really matters in the long run . I prepared every year and it helped me a lot even in the ISRO interview. The motivating factor to me was working in ISRO, that helped me a lot.

Now to the specific ISRO 2019 recruitment details:

OCT 2019 (Notification from ISRO)- 44 vaccany - This was a huge number and i was really happy. I thought this is my best chance to get selected and I have my past experience to learn from. I started preparing seriously by solving ISRO previous years and mocks as well.

May 2020- I was working and saw a notification in Gateoverflow that isro has declared the result. As usual i thought , no hope this time also. 108 till that time was my lowest in all ISRO written exams and going by ISRO written exam trend i would not qualify. I opened the result pdf with not much hope and searched my roll number. But expect the unexpected , I found the search to be showing 1/1 and i was dumbstruck to see my roll number in the selected list. The joy i had could not be explained. I was now determined to utilise the chance i got to the fullest.

May 2020- March 2021- It was one of the most uncertain period in my life. Covid came in , Work from home had started and I had to prepare for Interview. I started reading standard text books, read many interview experiences and joined many groups and prepared. But there was an uncertainty about how the interview will be done , online or offline and when will it be.

March 20, 2021 - I had chosen VSSC Trivandrum as my center. I had faced a lot of hurdles on the past day. The hotel i booked did not register my booking properly and there were issues . It made my confidence go down. But then I remembered it is all part and parcel of the game. The funny part is i forgot to wear a mask when i came out of my hotel. I felt my interview will be doomed . But somehow i managed to get one mask from outside and felt a sense of relief.

My interview was schedule on 11 am . I reached around 9.30 am. I entered into VSSC , it gave me goosebumps . I felt this is the do or die situation. When i sat in the waiting room , a lot of things flashed into my memory . 4 years of my gate preparation and a lot of other things. They called me around 12 to go to interview hall. I was waiting outside the interview hall and at 12:30pm I was called.

The next 25-30 mins was the best minutes of my life.

I am sharing the detailed interview experience below:

The interview was online this time.
I was asked to introduce myself and asked to tell my work exp , educational background and favorite subject. I introduced and told my favorite subject as OS,TOC,DS,Algo,COA. My preferred programming language was asked and i told Python and C.

I am not remembering the proper order of questions , and might have missed some questions also. Please dont mind it.I was told first TOC would be asked.

TOC

1) What is language

I was stuck for one second. But explained "A language is a subset of sigma star".

2)What is Sigma

3)Define DFA

Explained the five tuple form.

4) If NFA and Epsilon NFA exist , why go for DFA.?

I told NFA and Epsilon NFA is easier to construct than DFA. Also we have algorithm to convert NFA to DFA.

5)What is recursive language?

Expalined it using Total Turing Machine concept. I guess this was a game changer. I thank Kiran Kumar Pasupuleti sir for the teaching the TTM concept.

6)What is recursive enumerable language?

7)What is NP hard?

8)What is NP Complete?

9)What is halting problem of Turing Machine?

10)What is decidable language?

11) What is A^n B^n C^n?

I told it is CSG. But he was expecting the machine which accept it. I told its LBA.

DS

12)What is tree?

An acyclic graph which is connected.

13)What is forest?

14)How to make a stack using queue?

15)What is Binary Search tree?

16)What is AVL Tree?

I said i dont know about it.

OS)

18)Paging vs Segmentation?

19)What is Disk Scheduling algo?

I explained the FCFS, SSTF,SCAN, Elevator.

20)How can we avoid starvation.

I replied "increasing the priority of process".

Algorithm

22)Give example of Divide and Conquer, Greedy and Dynamic Programming algorithm

23)What is difference between Divide and Conquer , Dyamic Programming

25)What is inplace sorting algorithm and Not inplace sorting algorithm.

C programming

26)What is macros

27)What is inline function

COA

28)What is pipelining?

29)What are hazards

30)What is locality of reference?

31)What is write back cache?

32)What is write through cache?

CN

33)What are the layers of ISO/OSI?

34)Compare TCP and UDP?

35)In which port HTTP runs.

36)Example of UDP using Application layer protocol.

Machine Learning

37)What is Machine learning vs deep learning.

Expalined that ML need hand crafted features but DL extract features automatically. Explained some DL and ML algorithms

38)What is underfitting and overfitting.

39)What is k-crossfold validation

40)What is corelation vs covariance

(I replied i dont remember sir)

S/w Engg

41)Different stages of SDLC.

(Told me to just name them only)

42)What are different examples of testing.

43)What is regression testing

44)Good features of a s/w

They gave me hints. But I was not able to answer it

Compiler

46)Different stages of compiler.

I replied saying pre-processing, compilation. But he helped me saying that "not this. there are some stages during a compilation". I understood my blunder. I replied with all the stages.

47)What are the different examples of Code optimization.

I answered with some examples. But it was not completely correct.

DBMS

This was the last question. But since i did not prepare dbms i politely replied "I cannot recollect sir".

He said "OK . Thanks sandeep. Interview is over"

The whole interview went around 25-30 min i think.I felt it was like a rapid fire round. But in meantime they allowed me to drink some water. They tried to look at the breadth wise knowledge of my subjects. They asked questions even from outside of my favorite subject , but i answered it confidently. I guess this helped me a lot. My ML background also helped me i guess. After coming out of interview hall i felt i had given my best.

The next 5 months was very hard to pass by. The second wave came and our results were delayed.

Sept 3 2021- ISRO had given the tentative dates for the result as first week of September. Till evening 5 pm , result did not come. Around 6 , i got a telegram notification that result had come. My heart started raising and i opened the pdf. I started scrolling down from the bottom hoping that i might get at least a 44 rank. I kept on scrolling and reached the top. Then i thought i have not got selected. But then found my name on Top :)

Sandeep Nithyanandan - AIR 1 - Selected. My ISRO Dream has come true.

I literally cried after seeing this. All my years of effort has been finally approved. This was the Endgame for me and i succeeded. I would like to thank all my teachers who helped me in this journey.

I have met some very good friends.  Balaji Jegan  Mayank Raj Sajith Menon Akshay Kishore Parwateeswar Gollapalli. I would like to thank Habib Mohammad Khan Devesh Kumar Harshit Saxena Saurabh Shrivastava as they have helped and guided me a lot.

If you are determined and consistent , success will come. For me ISRO was my dream and i never gave up on it.
6
first search for how to apply for MS at IIT KGP. (it’s a complete different process)

There were different panelists with different domains, level questions keep increasing as you give the answers.

Q. What is BST?
Q. BST search complexity average and worst and when worst?

they’ll share a google doc with you to write on it as they can see it too.

Q. complexity of quicksort?
Q. write pseudo code for quicksort partition function?
Q write recursive call function of quicksort?
Q. Given this array, apply quicksort on this?
→ I totally did forget how to write partition, recursive code, even given a array I was not able to apply the quick sort on it, more because I tried to remember the quick sort solution I studied in coaching, but professors will keep supporting you, so I decided to build some new algorithm for it and developed a new algorithm for quicksort there.

Q.  How to dynamically allocate 2D array in C?
→ I don’t code in C, so told them and they were fine with it,

Q. write on the doc big Oh notation of functions.
Q. what if they f(n) and g(n) are equal.
Q. write mathematically f(n) = O g(n)
→  f(n) =< C g(n) for all n>x , need to find x given a C
Q. lots of discussion on this finding x and C?
→  not how to find it or finding them, but what to do the f(n) is equal to g(n)
→ i think i messed up here too, gave a 50-50% sure not sure answer

Interview ended.
on the same day, I received an email stating my performance was decent but for satisfying and a 2nd round of interview is being scheduled for me after 2 days. I prepared well in those 2 days, there was no sorting, searching algorithm i can’t code now, jokes apart, prepare your gate notes for DS and algo, that’s enough.

Q. Given an array find and X find pair in array whose sum is X?
→ i was happy it’s pretty standard question you would find in every preparation. they want you to start with a naive solution and then optimize it, I stated the naive solution and gave it’s complexity as n^2, and quickly wrote it’s code on the shared doc,
→ I knew the solution for O(n) but still din’t gave the answer right away
→ Then gave a optimized solution with hashmap and wrote its code which theoretically should give O(n) but was giving O(n^2) still because of searching in hashmap.keys() returns a list, I replaced it with set which again gives O(n^2) because of forming set everytime, you can use add element to set also which won’t give O(n^2), somehow we ended up to O(nLogn) as used binary search also, and i ended the discussion with the best solution i knew with O(n). believe me O(n) is the solution you’ll find in most of competitive course or website for this problem, but the professor gave me some more hints and was able to solve it in O(1), haha, shocking.

Q. asked I code for graphs, I told NO, he was happy i said NO so he can ask question on it only, Find the greatest distance can be covered in a given graph,
→ well i was not able to solve this and professor skipped it as i took lot of time.

Q. We have a problem of size N and it is divided into “b” subproblems and from those b problems we only solve “a” number of subproblems , and each problem take O(1) to solve, write recurrence relation for it.
→ never saw a question like this but as i prepared the gate notes just a day before I got the concept and solved it in seconds .

Q. In the formed recurrence relation give an example (name of algorithm) where a=b?
→ gave answer as quick sort.
Q. give an example (name of algorithm) where a!=b?
→ I had no ideas about it, after a hind i gave a right answer binary search.

Interview ended
this interview went nice. and got selected,
7
I’ll be quick,

Q. tell me about yourself ?
→ talk more about your projects, not anything else, they’ll simply ignore anything else. If you mentioned a lot of new technology in it, your interview might run on its way, for me, I kept it in the direction of what subjects I prepared.

Q. what subjects you prepared?
→ mostly DS, algo, OS, linear algebra is sufficient.

Q. What is Rank in a matrix?
→ some follow up questions on it

Q. What is BST?

Q. Explain NP problems?

DONE.

Result → selected
yup that’s it, it was simple, they really don’t want you to fail in it, they’ll stay with basic, rather too basic definitions, selections of students is very ambiguous but, the student with score 550 was also selected (gave interview much better) and student with score 650 was also rejected. Truth be told the student with a 550 score had a better understanding of subjects and concepts.
8

Research Stream Preference: Intelligent Systems (background subject: linear algebra and probability theory)

There were three professors in the panel, only two of them asked me questions. I will refer them by I1 and I2.

I1: Read out my application, mentioned my GATE score and rank, department preferences, labs selected, and asked about my BTech CGPA

He asked me why I did not apply for direct PhD and explained me benefits of doing direct PhD.

I1: What are the subjects that you have prepared for the interview?

Me: Sir, I have prepared background subjects linear algebra and probability, and familiar with subjects in GATE syllabus.

I1: I will ask you questions in probability first. Tell me if you have referred any standard book for probability?

[I mentioned the Sheldon Ross book]

I1: There are two types of random variables: discrete and continuous. Can you tell me what is the difference between the two random variables?

Me: For discrete random variables the values that the random variable (X) can take are countably finite and for continuous random variables the values are uncountable.

I1: (He was not impressed with my answer) Are you sure that is the correct statement? And is it written in Sheldon Ross book?

I1: Why do we name it continuous random variable? Why not call it uncountable random variable?

(We had discussion about this for about 5 minutes then he said that we call it 'continuous' because the cumulative distribution function for the random variable is a continuous graph.)

I1: Coming to normal random variable, can the peak of the bell curve have value greater than 1?

Me: The sum of probabilities in the range will give the total probability = 1. So total area under the curve should be 1. But I am not sure if peak could be greater than 1.

(Interviewer was not convinced with my answer. He gave me a few hints but I couldn't answer it well)

I1: What will be the value of normal random variable for $X = x$

Me: $P(X=x) = \frac{1}{\sqrt{2\pi \sigma^2}} e^{\frac{-(x-\mu)^2}{2\sigma^2}}$

I1: Right. What will be the maximum value for this? (assuming mean=0 and std=1)

Me: $\frac{1}{\sqrt{2\pi}}$ at x=0.

I1: Tell me about the binomial random variable.

Me: Told

I1: Can you say that binomial random variable is a limiting case of normal random variable? (If n is very large then will the binomial random variable become similar to normal random variable?) Prove it.

Me: I said yes but I couldn't prove the statement.

Now, the other professor took over and asked me questions on linear algebra

I2: What are eigenvalues and eigenvectors, can you define them?

Me: Sir, these are vectors whose direction remains unchanged after transformation. They might squeeze or stretch but the direction remains unchanged.

I2: Can you write the equation that you would use to calculate the eigenvalues and eigenvectors. And also explain the above definition with respect to that equation.

Me: Told

I2: Do these eigenvalues exist for every matrix mxn ?

Me: No sir, they are defined for only square matrices.

I2: Yeah, can you tell me why?

Me: In $Ax = \lambda x$ if A is rectangular matrix (m, n) and x is a (n, 1) column vector then Ax would be m-dimensional column vector (m, 1) which is different from RHS, i.e $\lambda x$ is a n-dimensional column vector (n, 1).

I2: Can you workout the above equation and show me how you will go about calculating the eigenvalues.

Me: $Ax = \lambda x$

$Ax = \lambda I x$

$(A-\lambda I)x=0$

$det(A-\lambda I)=0$

Now, we will solve for $\lambda$

I2: Okay, I understand the first two steps but why have you made $det(A-\lambda I)=0$ in the third step.

Me: Since we have $(A-\lambda I)x=0$. To solve this equation, x represents some combination of column vectors of $(A-\lambda I)$ that equate to zero. So the column vectors are not independent and hence the rank would be less than n. That would mean the determinant of (n x n) matrix should be zero if we want a non-trivial solution.

I2: Okay, now suppose I take transpose of A. Will the eigenvalues change?

Me: No sir. If $det(A-\lambda I)=0$ then $det((A-\lambda I)^T) = 0$ because the determinant remains same after transpose. Now, $det(A^T-\lambda I)=0$. Hence, the eigenvalues $\lambda$ will remain same.

I2: Okay, so you said that determinant remains unchanged after transpose. Is that true for every matrix?

Me: Yes, sir

I2: Do you know about row echelon form or reduced row echelon form. Can you name some common matrix operations?

Me: Yes sir, we can exchange two rows/columns, we can subtract/add multiple of some row/column and add to the other row/column.

I2: What would happen to the determinant if we apply these transformations.

Me: Sir, the determinant would remain unchanged.

I2: Can you take a simple matrix and show with a simple operation that determinant remains unchanged?

Me: I tried to work out a proof with a simple 2x2 matrix but couldn't clearly do it. He did give me some hint. Later I showed him an example that in a 2x2 matrix if we do $R_2=R_2-3R_1$ then the determinant value remains same.

(He was looking for a formal proof but I couldn't do it due to panic so I just showed him a simple worked out example by taking a 2x2 matrix)

The interview ended here, it lasted about 45 minutes.

My suggestion to future aspirants will be to prepare the topics from standard books right from the start of their GATE preparation. The interviewers focus on concepts and proofs which are very well explained in the standard books.

Verdict: Not Selected

9

## 7 General MCQs (5.0 marks each)

1. There is lockdown due to covid.

Ram and Gopal have decided to meet at a bus stop between 2PM to 3PM. At the bus stop a person can wait only upto 15 minutes.

If a person comes to the bus stop, he will wait for 15 minutes, or upto 3 PM, or till the other person comes up, whichever event happens earlier.

What is the probability that Ram gets covid given that Gopal is covid positive?

a. 3/4

b. 3/16

c. 1/4

d. 13/16

2. Consider 3 equations -

$x-y+2z = 1$

$2x-y+7z=2$

$-x+2y+z=b$

where 'b' is an integer. Which of the following is true?

a. The system has no solution if b=-1

b. The system has more than one solution if b=-2

c. The system has no solution if b=3

d. None of the above

3. Given a spam email detector. It detects if the email is spam or not by checking the subject line "Read this email!". If the subject line matches then the email is detected as a spam.

It is known that 4 out of 10 emails are spam.

1 percent of the spam emails have the subject line "Read this email!"

1 out of 250 non-spam emails have the subject line "Read this email!"

Find the probability that an email is spam given that spam detector marked it as spam?

a. 0.33

b. 0.625

c. 0.25

d. 0.0125

4. Given two column vectors u and v of size n each.

$W = uv^T + vu^T$

$X=u^Tv+v^Tu$

Which of the following statement is true?

a. The matrix W and matrix X are scalar.

b. The matrix W is a scalar and X is nxn.

c. The matrix W is always symmetric and nxn and X is a scalar.

d. The matrix W is nxn and X is a scalar.

5. Given a program to print the nth fibonacci number.

*A simple program to print the nth fibonacci number was given.*


What is the time complexity to find fib(n)?

a. O(n)

b. O(n^2) – This was an error in the options, it should be O(2^n)

c. O(logn)

d. O(nlogn)

6. Given $u=[a \ b \ c]^T$ and $A=\begin{bmatrix} a^2 & ab & ac \\ ab & b^2 & bc \\ ac & bc & c^2 \end{bmatrix}$is a 3x3 matrix $A=uu^T$. Given that a, b, c are all non zero real numbers. Which of the following statement is true about matrix A?

a. The matrix has three nonzero eigen values.

b. The matrix has two complex and one real eigen value.

c. The matrix has exactly two nonzero eigen values.

d. The matrix has exactly one nonzero eigen value.

7. Given a graph of a function f(x).

The graph of $f(x-1) + f(x-4)$ will be:

## 2 Programming Questions

1. Write a program to print the given matrix in clockwise spiral order. (10 marks)

2. Write a program to check if a matrix is diagonally dominant. (5 marks)

A matrix is diagonally dominant if for every row of the matrix, the magnitude of diagonal element is greater than or equal to the sum of magnitude of all non-diagonal elements of that row.

Note: The matrix contains values of type float.

10

Hello everyone.I hope you all are doing well.

Here are my GATE 2021 credentials:

Name-Akshat Kumar

GATE Paper:CS/IT

Rank-206

Score-798

Category-Non EWS General

B.E/B.Tech branch-Printing Engineering

Since I had less chances of getting CDS coursework and was anyway somewhat more inclined towards research, I decided to apply for MTech research.

Firstly,candidates where shortlisted based on their GATE scores for the written test which would be used to shortlist for interviews.Unlike 2020 where cutoff was an astonishingly high 845 GATE score for written test, this year the cut off was a generous 700.

I don’t exactly remember the questions but there were 9 MCQ questions,7 Mathematics(Linear algebra,Probability,Graphs) and 2 Programming.

7th May,2021: Written test:

1 question was on graph plotting,1 question on Baye’s theorem, 2 questions based on Eigen values, 1 question on general probability and 2 questions had all options incorrect as far as I remember. For programming, there was 1 question on spiral traversal of matrix and another was called Dominant Matrix in which we had to find number of rows in which magnitude of diagonal element  was greater than magnitude of all other elements in the row.

The test was conducted on HackerEarth Platform and was 1 hr 15 mins in duration.I attempted all questions except spiral matrix as I didn’t have much time left.

I was shortlisted for interviews after which we had to fill our lab preferences.I filled VCL AND BCL(Visual computing and Biomolecular computation labs). We also had to give Statement of Purpose for each of the labs we wanted to join.

17th May,2021:Interview:

The interview was conducted over Microsoft teams.There were 4 professors in the call.Here is my interview (Ix=interviewer x):

I1:Read out my application form details like GATE score, B.E degree and Labs preferences.

Me:Confirmed

I1:What topics have you come prepared for Akshat?

Me:Sir, linear algebra,probability,DSA and image processing basics.

I1:Starting with linear algebra.Can 2 matrices with different elements have same eigen values?

Me:(after thinking for a moment)Yes sir,

I1:Can you give me an example?

Me: Gave example by keeping major diagonal elements same and using favorable minor diagonal elements,sometimes making Minor diagonal product zero and sometimes making one of the elements as 1.

I1:That is a pretty good example.This is a property of matrix. We write it as A=PBP^(-1).

Me:Oh yes.Isn’t this condition for diagonalizable matrices, sir?

I1:Yes,good observation.Now can you prove that the two matrices A and PBP^(-1) have the same eigen values?

Me:Asked permission for using pen and paper and started thing along the equation A.X=lambda.X

After few minutes I was able to prove this and showed the solution on camera.

I1:(quite impressed)That is a really good proof. I2 now you can ask him questions.

I2:Are you comfortable with probability?

Me:Yes sir.

I2:Ok,suppose you are in a class of 30 students,what is the probability of having a birthday common with atleast 1 student in the class?

Me:Again used pen and paper.Thought in terms of discrete random variables.Say X represents number of students with whom I have a birthday in common.So basically I need to find P(X>=1) which is same as 1-P(X=0).

P(X=0)=(364/365)^29

So P(X>=1)=1-(364/365)^29.

I was also narrating my steps to I2 while solving.So I gave answer like this.

Me:Sir its a difficult calculation but would be close to 0.99.(Realized my mistake immediately and corrected)Sir actually 364/365^29 is close to 0.99 so probability would be something like 0.01 .

I2:Ok.So now suppose we have 400 students instead of 30.Would the probability increase or decrease?

Me:(A bit confused)Sir i think it would decrease.

I2:Are you sure?

Me:(Realized)No sir, actually since the number of students have increased, there is higher chance of having a common birthday and also 364/365^399 would yield a smaller value so 1-364/365^399 would have a larger value.

I2:Ok good.I3,would you like to ask some programming question(probably because my B.E was in printing XD).

I3:Yes.So can you write a program to find largest and second largest numbers in a given matrix.

Me:Yes sir.First I wrote a code finding largest in one pass and second largest in another pass and narrated the logic to I3.

I3:Ok that’s fine,can you optimize it, like try to do this in one pass.

Me:Did that.And showed the psuedo code on camera.

I3:Ok good.I4 do you have any questions?

I4:No I am fine.

I3:Ok Akshat.Your interview is over.We will now disconnect the call.

Me:Thank you sir.

My interview lasted only about 18 mins including introductions and salutations, which was relatively short,probably because I didn’t struggle much with any of the questions(not boasting).Overall, interview was great and it felt great to be interviewed by the best minds fro one of the best research universities in the world. The professors were very friendly and as far as i felt, will always guide you through if you are stuck with some question.I would definitely recommend Gilbert Strang’s MIT OCW lectures on linear algebra to be thorough with theoretical understanding of the same.First 15 lectures should suffice.

26th May,2021:The provisional shortlist was released and my application number was on the list.I was really happy but still had some fears since there is always some chance that you may not make it to the final list although such chances are less if your interview went quite well like mine.

10th June,2021:Received offer letter in mail at 7:09PM. My happiness  knew no bounds.From B.E in Printing Engineering to AIR 206 in GATE CS/IT followed by M.Tech Research at IISc CDS, what a journey this has been, I imagined as I watched my parents shed tears of happiness :’) .Thank you all. I hope I helped you somewhat and hope to see many of you at IISc next year.Cheers. :D

11

For 2021 Selection Criteria for IISc CDS: GATE score 70% + 30% written test and interview

Written Test Questions [Total Marks: 40]:    (Time: 1 hour 30 minutes)

There were 5 MCQ Questions, each carrying 5 Marks [5x5=25] from the domain:

• Linear Algebra (Especially, basic properties of different matrices and eigenvalues)
• Probability (Classical)
• Combinatorics
• Graph Plotting

There were 2 Programming Questions [5+10=15]:

1. Check if the input array is in strictly non-decreasing order or not. [5 Marks]
2. The input sample Matrix M is of size n x n. Given, Filter Matrix W is of size m x m. Perform Convolution and find out the output matrix C of size (n-2) x (n-2). [10 Marks]

12

Primary Interactions:

• First, they have read out my application, asked about the choices and preference order of departments.
• Next, they asked me about my future plans and favourite subjects.

Questions:

1. All the elements of a NxN matrix are 1. Can you guess at least one eigen value, quickly? Give reason in support of your answer.
2. I is an identity matrix of size NxN. U is a column vector of size Nx1. It is given, $U^TU\neq O$ and $UU^T$ is of size NxN. The following equation holds: $[I - \alpha [UU^T]]U = - U$ where $\alpha$ is a scalar. Find the value of scalar $\alpha$ and also show the derivation.
3. Write an efficient algorithm to find out the multiplication of a Diagonal Matrix and an Anti-diagonal matrix of size NxN.
GATE Score (2021): 646
GPA: 9.53 (Linear Average upto 6th Semester, during the time of interview)
Category: SC
Result: Selected
13
My gate score 593

Btech percentage was 81.38. the cutoff for self sponsored category was 80% in BTech.

My interview was on Webex,Their were two professors in the panel.

professor 1:

1. tell me about yourself? ( told and i also told them about my fav subjects algo , os and linear algebra)

2.you are given an array of length 'n'. How will you find the maximum and minimum element in the given array.( they shared me a link , where I had to write the pseudocode of this.)

3.what is Bankers algorithm?

4.will there be a deadlock if system is in unsafe state?

5.what is the fundamental difference between a Process and a Thread?

6.in which direction heap and stack grows?

Professor 2:

1.what is big O notation? can you formally define what is the big O of a function?

2. what is the time complexity of Dijkstra's algorithm?derive.
14
I am Revanth ,with Gate Rank:2836 and Score-561 Category -GEN-EWS

IITJ has above 600 cutt off for with fellowship Category or Via COAP- so I applied via self sponsored mode for CS and With out Fellowship for AI I got shortlisted for both categories and both interviews happened at same time.

Interview Experience,

1-  Introduce Yourself ?

2-  What is your preference CS/AI ?

3-  Programming question-Find Second Largest Number in Array on Single Go(Single For Loop Logic) ?

4- What is Use of Pointers ?

5-  What is Difference Between Primary and Secondary Memory ?

6-  What is Fastest Memory in Computer System ?

7- What is Bayes Theorem?

Note- They did not ask me about Favorite subjects in the beginning they directly jumped to ask Questions.

Cutt off:

Self Sponsored CS  >70 for Gen-EWS

Without fellowship -CS- >540 for Gen-EWS  and  AI – >465 for Gen-EWS
15

I received an email on 14th May from the program coordinator at IIT Indore saying that I had been shortlisted for the interview round. My interview was scheduled for 17th May between 2:30 PM to 5:30 PM.

Now, after my GATE results, I was a little heartbroken knowing that I wouldn’t make it to the IITs but I had consoled myself with the hope of getting into something like IIIT Bangalore. When I got the email though, I quickly realized that I was very ill-prepared for any technical interview as I had not studied anything GATE-related after 13th February. So I took a one-day leave from an internship I am doing and started going through GeeksForGeeks and this site to prepare DSA and OS over the weekend.

From OS, I mostly studied deadlocks and I went through some typical competitive coding problems for DSA. Little did I know what was in store for me.

Fast forward to 2:30 PM on 17th May. I wore a shirt and sat down in front of my laptop. The call came at 3:45 PM and the person on the other side informed me that I was going to be sent a Google Meet link and to join it after a second call. The second call came at 4:30 PM.

When I joined, I saw 4 people in the panel. Everyone’s mics and camera were turned off except for the mic of the main interviewer (we’ll call him P1), who I recognized as the admission program coordinator. The two others were professors and the fourth person was the one who called me.

P1: Hi Anirban. Give us a short introduction of yourself.

Me: (Talked about who I am, my current educational background and why I want to pursue research in AI, and what I have done so far)

[My project is based on using Computer Vision for ad detection. I spoke about it in detail and the interviewer seemed quite interested. For the next 10 minutes, we discussed only this. He asked me for details about how I implemented some things and what error detection measures I had built in. Basically, we had a nice conversation about my project and in the end, he even suggested some ways in which I could make it even better.]

P1 : (gesturing me to the second interviewer). Sir, would you like to ask any questions? (Handed me over to P2)

P2 : So are you familiar with the faculty at IIT Indore?

Me: Yes, sir. I know that (named two of the interviewers on the panel, one of them being P1 himself) have published some incredible research papers in the field of image detection AI. (I also knew that P1 had worked with biometric verification using AI methods, so mentioned that).

P2 : Okay, great. (Handed me back to P1)

P1 : Okay, Anirban. So can I ask you a simple maths question? (I said yes). Okay, so imagine you have a dice and the probability of getting a 1 is p, the probability of getting a 2 is p², and so on. How do we calculate the value of p?

Me : (Answering that it would be a geometric progression equation where p+p²+p³+….=1 and then we can use the sum of GP formula to shorten it. Was about to try to solve it on paper when P1 said….)

P1 : Okay, I think you get the idea. (Told me a method to solve for higher polynomial powers). Do you have any questions for us?

Me : (Asked about what material I should follow to further my knowledge in image processing AI. I mentioned that I already have some personal projects and an internship, and about how I am trying to learn Linear Algebra in-depth from Gilbert Strang’s MIT OCW series and its applications in AI)

P1: (Told me how I must never forget the basics of AI and neural nets, and to solve sums for the Gilbert Strang book to make my Linear Algebra stronger. Finally….) Thank you, Anirban. You may disconnect now.

So that was my interview and I got the offer in the first round. My main take-away for those aspiring for a master's in CSE is that the subjects in B.Tech or GATE should not be your end-all-be-all. If you are going for masters for anything other than purely placement reasons, be sure to invest some time pursuing Machine Learning or Competitive Coding or Full-Stack Development, or whatever it is about Computer Science that you’re interested in, during your B.Tech years. Not only would you be better suited for placements if that’s what you wanna go for but it will also greatly help boost your chances in master's interviews and give you a decent head-start in your curriculum ahead.

I prepared for GATE starting from April 2020, without any coaching or even standard books. I learned pretty much everything that I needed to know from Gate Overflow, GeeksforGeeks, Stack Overflow, and free RBR lectures. Now would I have secured a better rank with formal coaching? Maybe. But I didn’t want to be spoon-fed stuff in a classroom to learn something that I knew I could learn by myself for a fraction of the cost and at my own pace. All told, my total investment behind GATE is about Rs. 2000. 1500 for MadeEasy + AceAcademy test series and 500 for a 30-years GATE question bank from Amazon.

16

Greetings to all, I am Animesh. I have appeared in GATE 2021 and my gate score was 742 with a rank of 447 General Cat. Here I am posting various questions asked from me in different interviews for MS/M.Tech Research courses.

Note: My interest lies in Machine Learning and AI, that’s why I prepared Linear algebra along with basics of ML for these interviews.

1. IISC Quantum Technology M.Tech interview questions : https://docs.google.com/document/d/1E9Ta_1zm8nvktaWcKOchMDTh3BWQ-kf2KGilubRlpJc/edit?usp=sharing [This was a new course started by IISC this year(2021), and I had no prior experience in this Quantum Tech field, so I appeared in this interview just for the sake of experience]
2. IIT Bombay MS TA interview questions : https://docs.google.com/document/d/15A4SsQsc5diSsP6gxR73joAY8yUo6mVGXcYHk6Yy-nQ/edit?usp=sharing

I will be adding few other interview experiences(IISC CDS, IIT Bombay MS RAP etc) soon.

17

Some memory based questions:

1. Time complexity to find the maximum element in the min heap and explain the method?
2. Given an array of length $n$ and a number $x$ find out two such elements in the array such that their sum is equal to the number $x.$
3. Given an array of length $n,$ find two numbers such that their sum is equal to the rest of $n-2$ elements if there exist such case?
4. Two linked lists are given and due to programming error end node of first linked list is now pointing to some node of second linked list, how will you find that node? and you don't know which one is $1^{\text{st}}$ linked list and which one is $2^{\text{nd}}.$ The data values are not distinct.
5. Define joint probability in terms of conditional probability?
6. How will you find a cycle in a directed graph? some questions on forward edge and back edge.
7. Sort an array of $n$ elements with k distinct elements optimally. How will you find the distinct elements in the array optimally
8. A $n\ast n$ matrix is given such that $A_{ij} = A_{ji},$ what will be the rank of this matrix?
9. How many different values a random variable can take with zero variance and why?
10. Prove that a directed acyclic graph has atleast one vertex with zero indegree.
11. Various ways to solve subset sum . Variations of the same problem.
12. Algorithm to get maximally connected graph having two components.
13. Suppose we have $A\ast B.$ If we know determinant of $A$ is $1.$ What can we tell about Rank of $A\ast B$ in terms of $B.$
14. Give $O(k\log k)$ algorithm for finding $k$ minimum element.
15. Prove two vertices of a graph have same degree.
18

Bharati Padhy, $\text{Gate}\; 2020, \text{GS-}624, \text{AIR-}1531, \text{Jest}\; (2020)\; \text{AIR-}75$

Some memory based questions:

1. Yourself
2. Write a program to find the $2^\text{nd}$ minimum number from an array in one pass.
3. CMMI Levels
4. Difference between Production environment and Deployment Environment.
5. You have given some ingredients and you have to make a recipe out of it. Using graph theory terms explain this scenario how you will do it.
6. If a matrix is invertible then what can you say about it. How to take inverse of a matrix
19

Bharati Padhy, $\text{Gate}\; 2020, \text{GS-}624, \text{AIR-}1531, \text{Jest}\; (2020)\; \text{AIR-}75$

Some memory based questions:

1. Yourself
2. Why Data Science?
3. If you have n numbers how many bits are required to present that numbers?
4. If you have a matrix of $3\times 3$ which is not invertible then what you will say about the Rank of that matrix.
5. How many probability distribution function are there which you know?
6. Explain Binomial distribution? Mean and variance?
7. In which distribution Mean and variance are same?
8. You have given a number; you have to find the number of digits which are divisible by $3.$ Eg. If number is $123$ then it should return $1$ as output as only $3$ is divisible by $3.$
9. What is the complexity to find a number from BST.
10. You have a bidirectional graph max number of edges in that graph?
11. You have $2$ events $A$ and $B. P(A)=0.6, P(B)=0.7$ what you can say about it disjoint event or dependent? Axioms of probability.
12. There is a person $A,$ who has $2$ kids. If the first child is girl then what is the probability that $2^{\text{nd}}$ child is also girl.
20

Bharati Padhy, $\text{Gate}\; 2020, \text{GS-}624, \text{AIR-}1531, \text{Jest}\; (2020)\; \text{AIR-}75$

Some memory based questions:

1. How many Prime numbers are there in universe?
2. How will you prove that there are infinite prime numbers?
3. You have given an empty stack which can hold atmost $3$ elements, what will be the top of stack after following operations: Push $6,$ Push $4,$ Push $1,$ Push $5,$ Pop, Pop
4. n=10
Fun(n)
{
while(n>0)
{
printf(n);
Fun(n-1);
}
}

5. How many maximum regions will be there when we draw $19$ lines on the plane?

6. You have a binary tree with $n_{1}$ vertices of degree $1, n_{2}$ vertices of degree $2, n_{3}$ vertices of degree $3.$ Explain $n_{3}$ in terms of $n_{1}$ or $n_{2}.$

7. do {
sum=0,i=0;
i++;
sum+=i;
}
while(i<5)
printf(sum);