Detailed notes for every InternHack reel: real-life system design, mock interview answers, diagrams and ready-to-use interview answers. With sources.
System Design · · 11 min read
The full FASTag system design: what's actually on the sticker, how the barrier opens without the bank, the NPCI and bank flow, failure cases, and how to explain it in an interview.
Interview Prep · · 8 min read
How to prevent payment double charges: why a timeout doesn't mean failure, why the common answers fail, the full idempotency key design, 409 vs 422, and the answer to the server-crash question.
