Physics Wallah - Staff Backend Engineer - Sept 2026
Summary
I interviewed for a Staff Backend Engineer role at Physics Wallah, went through four rounds including DSA and system design, and received an offer.
Full Experience
Company: Physics Wallah Role: Staff Backend Engineer
Current Org: Small Startup College: Tier-1 YOE: 8+ Current Comp: 60L Base + 5L Bonus + 20L ESOPs per year (will not materialize to any value)
Screen Call With HM Current project discussion, role details, and team details.
Round 1 - DSA Longest increasing sequence in an integer array.
Round 2 - HLD Design an experimentation/feature flag system. Scale: 2M requests per minute to check variants.
- Called from internal services, though better to call via client library.
- Use a consistent hashing-based approach to assign variants to users.
- Use client and CDC to propagate changes to client libraries.
Round 3 - HLD Design an E-book store service. Scale: 6M concurrent reads for a book on launch.
- Users can add and purchase books.
- Focus: Users cannot download books locally. They can only see a set of preview pages and cannot access content for books not purchased. Some books are free.
Round 4 - Senior VP Round Project decisions - deep dive into a hardest tech project. How to optimize this for more scale. Some tech decisions on databases, networking, and SQL vs. NoSQL use cases.
Verdict: Selected.
Comp: Just matching current comp, not giving any hike.
Just figuring out next steps now. My current startup is likely shutting down soon, so I need to decide if I should just take this or keep looking.
Interview Questions (3)
Longest Increasing Subsequence
Given an integer array, find the length of the longest strictly increasing subsequence.
Design an Experimentation/Feature Flag System
Design a system that provides feature flag/experimentation capabilities. The system must handle 2 million requests per minute to check variant assignment. It should be callable from internal services, preferably via a client library, use consistent hashing to assign variants to users, and propagate changes to client libraries using CDC mechanisms.
Design an E‑book Store Service
Design a service for an e‑book store that can handle 6 million concurrent reads for a book at launch. Users can add books to a library and purchase them. Users should only be able to view preview pages of books and cannot download full content unless the book is purchased. Some books are free.