I recently interviewed for a 6-month Core Intern position at Tower Research Capital, through my campus placements cell. In this post, I will try to share my whole experience, including the Online Assessment (OA), technical interviews, and what ultimately made me stand out and get the offer. Hopefully, this will help you prepare better for their interviews.

The Role and Application Process

The role TRC offered was for a Core Intern position, specifically for the Post-Trade team, which looked for people to work on backend data management systems using Java, Python and shell scripting. They were open for students in the discipline of Computer Science and Artificial Intelligence, and required a CPI/CGPA of more than 8.5.

Fun Fact: I missed the application deadline initially, but was able to apply a day later by directly contacting the placement cell.

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Online Assessment (OA)

TRC’s OA was conducted on-campus on the HackerRank platform. It was 2 hours long and had the following format:

No.	Section	Questions	Topics
1	MCQs	10	Core CS: OS, DBMS, Networking, OOPs, DSA
2	Coding	3	Dynamic Programming, Graphs, Trees

The MCQs were a mix of easy and moderate questions, and were mostly theoretical or “predict the output of the code” style of questions. Some attention to these topics during your summers would be enough to get a decent score here. The coding questions were of medium-hard difficulty, and required careful attention to the input data. They could be solved using any popular programming language. I will recommend completing Striver’s A2Z DSA sheet and practicing Contests to prepare for this section. Put more time in the Pros and Cons of the various Data Structures, Dynamic Programming and Trees/Graphs as they were the main focus for TRC’s selection process.
The shortlist came after 2 days, and 10 students were shortlisted based on our performance in the OA and our resumes. They also shared a preference order for interviews of the shortlisted candidates.

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Interview Day

The interviews were rescheduled from 9 AM initially, to an unusual 2 AM start on Day 0, probably to compete with other Day 0 companies and take the best candidates. It was definitely a unique experience! Despite the odd timing, the process was smooth and consisted of 2-3 rounds with the Senior Manager as well as the Head of the team.

First Round

The first round started with a friendly introduction. Since I mentioned my projects and experience, the interviewer was keen to discuss them even before moving to DSA, and we had a short talk about Spring Boot. This made the conversation comfortable and engaging.

DSA Problems

1. Design a list like data structure that supports insert, delete, search at specific indices of the list, in $O(\sqrt{n})$ time.
2. A variation of the question Building Bridges, where the arrays represented the heights of pillars, and bridges can only be built between pillars of same heights.
3. Variation of the question Find the Town Judge, where we have to find the answer in a single pass over the adjacency matrix.

I was able to solve only the ${2}^{nd}$ one completely by myself, while I needed help with the ${1}^{st}$ and ${3}^{rd}$ questions. The interviewer was very sweet and helpful, guiding me through the process. I think the most important takeaway from this round was the importance of collaboration and thinking out loud about the different approaches, rather than just getting the right answer.

Java Questions

The interview asked me if I knew about Java’s String Pool, and since I was not very familiar with it, the interviewer opened up an online Java compiler on his laptop and explained that it is a special memory region where Java stores string literals. This helps in saving memory and improving performance.
He then asked me about the difference between .equals() method and == operator in Java. It’s important to have a learner’s attitude if you aren’t familiar with a concept and to be open to learning.

Project Discussion

After the DSA round, we returned to discussing my projects. The interviewer asked questions about Java, Spring Boot, and basic design principles. This part felt more like a conversation than a grilling session, and even though knowing Spring Boot isn’t an absolute requirement, having a solid understanding of its concepts and a project with it is beneficial. We talked about the MVC architecture, dependency injection, and the repository pattern. He then asked me about database sharding, and the difference between horizontal and vertical scaling.

The interview ended on light-hearted note, and I asked him about any ‘surprises’ he had encountered while working at Tower Research. Everyone received a bag of goodies as well, which included TRC branded Crossbody bag, notebook and a steel tumbler.

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Second Round

The second round took place 10-15 minutes after everyone’s first round was done and was conducted by the Senior Manager for me. This round started with a problem solving session and then moved on to experience and project discussion and OOPs based system design problems.

DSA Problems

1. From a list of numbers $arr$, find the first number, from $[1, 2, 3, \ldots, max(arr)]$ that cannot be made by summing up any possible set of numbers from the list $arr$. It was hard to understand the problem statement initially, but after some clarification and walkthrough, I was able to solve it.
   I initially approached it using dynamic programming, but the interviewer guided me to a more optimal greedy approach. The key insight was that if we can form all numbers from 1 to x-1, and the next number in the sorted array is <= x, then we can also form x by adding that number to some subset of previous numbers. If the next number is greater than x, then x is the smallest number that cannot be formed.
2. A Graph based problem, which I don’t remember exactly, but it was quite simple to understand and solve.

Project Discussion

We then talked about the project I made with Spring Boot, why I chose to make multiple microservices for the backend, and how I handled communication between them. I explained about some of the concepts of Spring like JPA, Hibernate, and Spring Security.

System Design and Operating System Problem

The interviewer asked me to use OOPs principles and design the File System for a typical Operating System. He wanted some functions like list and delete to work seamlessly on both files and folders.
I started by identifying a class hierarchy where the File class would implement an Item abstract class, which would also be the parent class for the Directory class. This would allow for shared functionality, such as getting the size and other attributes of a file or directory, while still allowing for specific behaviors in each subclass. Then we talked about how a file structure can be represented in the directory class. I first thought about Java’s different implementations of the List interface, like ArrayList and LinkedList. I then realised that a Tree would be the best data structure to represent the hierarchy of files and directories, and told him about making a Node class and storing the root node. I then talked about interfaces, explaining how they could be used to define contracts between classes.
He then asked if I can handle dynamically adding or removing functionality from the file system, to which I explained how I could use the Composition design principle to achieve this. This video by CodeAesthetic had helped me understand the benefits of composition over inheritance.
He asked me if I know about Databases, and asked how Indexing works, to which I explained the basic concepts of indexing, like B-Trees, and its importance in database performance. He then asked me if I have done any course on Operating Systems. I said that I’m taking it in the current semester and he was fine with it and did not ask any questions.

Finally, I asked him a question on whether TRC has any proprietary database system for their data since they mainly worked with time-series data only. He replied that they mainly used elasticsearch and other open-source tools only.

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Third Round

The Third round was conducted by the Head of the Post-Trade team. It was more of a informal discussion and was quite fast-paced. He asked me some good questions about my Spring Boot project and JWTs. We then discussed about 2 system design problems and ended with some advice for me.

Project Discussion

We talked about how I implemented JWT-based authentication in my project. He asked me to explain what JWTs are and how they work. I described the structure of a JWT, including the header, payload, and signature, and explained how they are used for stateless authentication. He then asked how the signature helps in verifying the authenticity of the token, to which I explained the role of the secret key in the signing process. He also asked me which encryption algorithms I used for signing the JWTs, and I initially forgot the name and said RSA but he pointed out that RSA is an asymmetric algorithm and then I correctly mentioned that I used HmacSHA256, which is a symmetric algorithm.

System Design Problems

We then discussed two system design problems. The first one transitioned from the JWT discussion, where he asked how I would design a system to handle user authentication using JWTs at scale. Firstly, I designed and explained a single JWTService class with Spring MVC Annotations and Spring Security features. We treated the exact implementation logic as a black box, focusing on the overall architecture. He asked me what I would do to scale the system to handle a large number of users and requests. I suggested using techniques like load balancing and database sharding to improve performance and scalability.
He then asked me to make a simple online book publishing system. He wanted the database schemas, and Service classes with relevant endpoints. I made a Users table with fields like id, name, and password mentioning that passwords should be hashed, and a Books table with fields like id, title, authorId, content, and is_published. I then created a repository class to have methods like getBooksByUserId(), getUser() and getPublishedBooks(). I also wrote service methods like publishBook(). He seemed satisfied and focused on optimising the way in which data would be handled in a real application.

He then mentioned some concepts and tools that I should learn to perform better in the internship (yeah, I was getting selected). He also emphasised on learning the core technology behind any tool and becoming a complete engineer. He ended the interview by saying that he was very interested in selecting me for the internship.

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Conclusion

After the third round, I was over the moon. The interview process had been rigorous, but I felt that I had showcased my skills and knowledge effectively. The positive feedback from the interviewers and their interest in my background gave me confidence that I was a strong candidate for the internship.
I met with the interviewers again in the breakout area, where I talked with the Head again to get his proper introduction, since he didn’t give one during the interview. They submitted their final preference list after a few hours, and I was thrilled and humbled to find out that I was their top choice.

Key Takeaways

1. The entire experience was challenging yet rewarding, and I learned that maintaining your composure and confidence is key during interviews. Make sure to prepare a strong and personal introduction for the interview.
2. A strong grasp of DSA fundamentals is essential. I prepared DSA by solving problems from Striver’s A2Z DSA sheet in my summers. You should actually start preparing early on if your goal is to crack an industrial internship.
3. Having a record of working on multiple good projects (good meaning projects that demonstrate a low-level understanding of systems development and also aligns with the industry), preferably outside of coursework, can significantly boost your chances in companies like Tower Research Capital, where interns are highly valued and actually given real work.
4. Needless to say, some experience with Java and enterprise frameworks like Spring Boot will definitely help you stand out.

I hope this detailed account of my interview experience helps you prepare better for your own interviews at TRC or similar companies. Good luck!