MobiKwik SDE-3 Interview Experience | Java Developer |

MobiKwik SDE-3 interview process was a mix of problem-solving, system design, and practical coding. Here’s a breakdown of the rounds and what I learned from the experience.

Round 1: DSA + High-Level Design (HLD)

The interviewer was polite and made the conversation comfortable from the beginning. We started with a brief introduction, discussing our backgrounds and previous work experience, before moving on to the technical questions.

Problem 1: Design an In-Memory Rate Limiter

The first problem was to design an in-memory rate limiter. Instead of jumping straight into the implementation, I started by explaining what rate limiting is, why it is needed, and where it is commonly used in backend systems and APIs.

Discussed different rate-limiting algorithms, including:

• Fixed Window: Limits the number of requests within a fixed time interval.

• Sliding Window: Tracks requests over a moving time window for smoother rate control.

• Token Bucket: Allows controlled bursts of traffic while maintaining an average request rate.

• Leaky Bucket: Processes requests at a controlled rate to smooth out traffic spikes.

After discussing the approaches, I moved on to implementing the solution. I was able to complete the problem in approximately 40 minutes and explain my approach to the interviewer.

Problem 2: Design TinyURL

Since the first problem was completed within the allotted time, the interviewer moved on to an HLD question: Design TinyURL, a URL-shortening service.

Discussed the major components required to build the system, including:

• Generating unique short URLs for long URLs.

• Designing the database schema and storing URL mappings.

• Handling collisions during short URL generation.

• Using caching to improve redirect performance.

• Scaling the system to support a large number of users and requests.

The discussion focused on the overall architecture, scalability, and trade-offs involved in building a reliable URL-shortening service.

Round 1 verdict: Strong Hire

Round 2: Low-Level Design (LLD)

The second round was conducted by a Staff Engineer. After a brief introduction, we moved directly to the design problem.

Problem: Design a Digital Wallet Using SOLID Principles

The task was to design a digital wallet system similar to MobiKwik, with a focus on object-oriented design and SOLID principles.

The discussion covered how to structure the application, define responsibilities for different classes, and create clean abstractions that would make the system easier to extend and maintain.

I worked on designing the core components and implementing most of the solution. I also focused on keeping the code modular and following good object-oriented design practices.

However, I couldn't make the entire implementation completely runnable within the available interview time. Although I was able to develop most of the structure and logic, I fell short of completing the implementation end to end.

During the feedback, the interviewer mentioned that my fundamentals were good, but I needed to spend more time strengthening my Low-Level Design skills.

Round 2 verdict: Not Selected

Final Outcome

I was rejected after the second round. The first round went well, but the LLD round highlighted an area where I still need to improve, particularly in translating a design into a complete, working implementation within a limited timeframe.

Sharing this experience so that others preparing for SDE-3 and Java backend roles can get an idea of the interview process and focus their preparation accordingly.