My interview was on 18th may as my registration number was even. People with odd registration number were called on 19th may.

Students were called for MS and M.tech. Prof. Sarang said that MS is their premier course. Interview will be conducted accordingly. MS interview will be difficult as compared to M.tech. According to him the difficulty of M.tech interview will be 5/10. and for MS it's 9/10.

they took interview in 2 slots. a.) 10:30- 1:00 b.) 2:30- 5:00.

they called in alphabetical order. so mine was in the 2nd slot.

Average interview duration was around 15-20 min. but if someone was not able to answer questions then it got over in less than 10 minutes too. my panel consisted of 2 profs.

prof: whats your fav subject.?(they asked this question to everyone.)

me: algorithms

prof: do you know quick sort?

me: yes.

prof: how it works? time complexity? recurrence relation?

me: I explained partition algorithm. explained all the cases. and recurrence relation too and also solved that.

prof: ok good. now do you know what is the median of an array?

me: yes. middle element of a sorted array.

prof: ok good. sorting takes O(N log N). but we have to find the median in linear time. how to do that?

me: use count sort algorithm for sorting and then find middle of array.(this is not appropriate answer in all cases)

prof: what is count sort and why quick sort is considered to be the best sorting algorithm.

me: explained count sort. and told its limitation.

prof: now assume that count sort cant be applied there. i.e applying count sort is costly for given array.now find median in linear time.

me: (after thinking for around 10-20sec.) we can use partition algorithm.

prof: they asked me to explain.

me: i explained it. i also explained recurrence relation as they asked for it too.

then they gave me a recurrence relation. and i solved that using recursion tree method. i got stuck while writing its general term. but they helped me in solving that problem.

prof: write structure of binary tree.

i wrote that.

prof: write a program to find product of leaves of a binary tree using recursion.

=>it was simple problem, initially i explained them how to find that. then i wrote the code. i missed one step which they pointed out. actually, I got nervous. I wrote the major steps(like the return statement, branch checking, whether the node is leaf or not, etc) but messed up in recursion step. Code was around 75-80% correct.

(their remark:

prof 1: programming thoda dheere krta hai.

prof 2: yha to bhut programming krni hogi.)

prof: you have an array in which initially elements are in increasing order and after that elements are in decreasing order. find the point where change occured.

=>i told them that i will use modified binary search here. they asked what is it?. i told them that instead of dividing n(size of the array) by 2. i will start with first element and keep multiplying it by 2. i.e i will search for 1,2,4,8,16 ..... they asked some que related to it. i.e how will you keep your search within array.? I explained all that.

this logic was ok. then they gave me a situation where the change occurred at a distance of (3/4)n. they asked me to run the algorithm which i suggested. They asked for its recurrence relation and time complexity.

i said O(logn). but they were not convinced and they gave me its recurrence relation acc to which ans was O(logn^2).

(but acc to me its still O(logn).)

note: applying simple binary search would have been better and conventional answer for above problem. I made my life difficult by using modified binary search.

prof: ok. we are done. send next student.

#mine interview went for around 30min.

As mentioned in IIT Delhi brochure, weightage is 70:30. (70% for gate score).

#they said that result will be announced in a week.

After interview i can say these things:

1. Profs are really cool. they will help you if you got stuck anywhere.

2. If you are preparing for IITD interview then algorithms and Mathematics is must. even if you say that your fav subject is COA they will definitely ask problems from DS or algorithms. So it's better to chose algorithms as your fav subject.

3. Only basic problems are asked. So its better to focus on basics.

4. Dont get nervous and try to answer problems in hurry. Take your time ,they provide enough time.

5. Your gate score is not a guarantee that you will get IITD for sure. you have to perform in interview too. they dont publish any formal sheet where interview marks and gate score are added in specified ratio.

Result: I got selected for M.tech. :)