This time IIT Guwahati organized an offline interview process for Ph.D. in Computer Science and Engineering, and candidates had to visit the college for the process. The whole procedure was comprised of 2 rounds where in the first round, we had a written test based on the GATE Syllabus, and the second round was the interview by the panel of professors.
Day 1 ( Written Test): Some 30 students in the seminar room came for the written test, and it was a 2-hour extended test comprised of 26 questions in a booklet that we had to answer and return to the invigilator. I opened the booklet and found questions based on GATE Syllabus and conceptual. They touched on almost all the topics in GATE Syllabus except compilers. Some of the questions from the written test that I have recalled are as such:
- Draw the process state diagram with proper labeling (Operating System)
- Given a max heap with some elements, we have to give the final array representation of the heap after inserting two elements. (Data Structures)
- One question from the optimal binary search tree where we have to tell a minimum number of comparisons needed to sort all the files (Data Structures).
- To write an algorithm to find the height of the binary search tree (Data Structures).
- Represent 11.25 in IEEE-754 format (Digital Logic).
- One minimization question based on the K-Map concept (Digital Logic).
- Give three characteristics of RISC Processors (COA).
- Give two methods to eliminate data hazards from a pipelining system (COA).
- One formula-based question finding the EMAT in a cache system (COA).
- Match the following questions on topics such as Computer Networks and Operating systems which were easy.
- Three questions from C programming. One is based on arrays, the second is based on recursion, and the third is based on functions.
- One question on the linked list.
- Draw a DFA which accepts all the strings not accepting 000 where the alphabet is {0,1} (TOC).
- Why is the recursive language called turning decidable? (TOC).
- One question on the closure property of regular languages (TOC).
- Find the number of page faults in the given memory references using LRU and FIFO (Operating System).
- One question based on MUX and one on flip flops (Digital logic).
These are some of the questions I remember. My exam went well, and I answered almost all the questions. Out of 30 students, they shortlisted 17 for the interview scheduled for the next day.
Final result: Shortlisted for the interview.
Day 2 (Interview): My interview was scheduled for noon. I went to the room where some 8 professors were sitting and was given a chair adjacent to the board. One professor was reading my application, my marks, and the college I attended. So, they asked me the topics I am confident in answering the questions. I told them I am comfortable with the Theory of Computation, Graph Theory, and Algorithms.
- The first question they asked was, ” Given n number of vertices in a graph, tell me how many maximum edges can be there in the graph ?”
- They told me to get on the board and asked me to give my intuition over this question. I made K4, checked the number of edges using the formula n(n-1)/2, and explained the logic behind this.
- The second question was, “What is a bipartite graph?” after answering this, they asked me whether the K4 I made on the board was a bipartite graph or not? Which I comfortably responded as it has an odd length cycle. It is not bipartite.
- Then they asked about matching problems and some real-life usage of matching.
- After that, one professor asked me to make a DFA for “name” and then for “see.” I made it on the board, and then another professor pointed out what if you have been given all the alphabet in the English language and you have to make a DFA that accepts all the languages that contain the substring “see.” I comfortably made all the DFAs on the board with proper explanation.
- Next, one professor asked me if I was comfortable with the Operating system, and I replied affirmatively. So, he gave me a choice to select which topics he wanted me to answer questions. I replied Deadlocks, Process Management, and CPU scheduling.
- I answered comfortably when he asked me the difference between Deadlock avoidance and deadlock prevention. He then asked what the methods are to eliminate circular wait from the system and how that method works. I told that we could label all the resource instances in ascending or descending order, and a direct acyclic graph would ensure deadlock could be avoided. He then asked me some concepts related to preemption.
- One question regarding the working of TLB and when a page fault occurs. That I explained with whatever my understanding of the topic was.
- He asked an outstanding question,” I have been given a dynamic round robin scheduling and the burst time of the processes is very big. All processes came to the system simultaneously. The condition is with every iteration of processes in the circular queue, the time quantum decreases by one unit. So, is it an optimal algorithm, or do we have to go with the standard round robin algorithm with static time quantum?”
- I made some calculations on the board, taking some dummy data and using a round robin algorithm. My points were more focused on the overhead due to context switching when the time quantum is decreasing with every iteration, and it is not an ideal way to schedule the processes.
The interview lasted 45-50 minutes, and I came out of the room. I was satisfied with my answers as I gave logical reasons for whatever they asked me.
Final result: Selected for the Ph.D. program at IIT Guwahati
I will spend my next years researching one of the most beautiful campuses in our country. I accepted the offer from IIT Guwahati. My area of interest is theoretical computer science and hardware architecture. Other offers I had before IIT Guwahati are from IIT Patna and IIT Jodhpur. I am a UGC-NET qualified candidate and awarded JRF from MHRD. I have also qualified GATE in Computer Science and Engineering.