Paytm Interview Prep ​
Read my intro — background, experience, and what I've worked on.
Company Context ​
Paytm is India's largest fintech platform — payments, wallets, banking, insurance, and lending at massive scale. The engineering bar is high on system design and clean code.
Interview Rounds ​
| Round | Focus | Time |
|---|---|---|
| Round 1 | Low-Level Design (LLD) | ~60 min |
| Round 2 | High-Level Design (HLD) | ~60 min |
Prep Notes ​
| # | File | Topic |
|---|---|---|
| 1 | 01-js-fundamentals | Closures, Promises, Currying, Polyfills, this, Prototypes, Hoisting |
| 2 | 02-design-patterns | Singleton, Observer, Chain of Responsibility, Strategy, Factory, Builder |
| 3 | 03-lld-problems | Digital Wallet, In-Memory DB, Caching Chain, Logger, LinkedIn Feed |
| 4 | 04-hld-system-design | CAP, SQL/NoSQL, Sharding, Caching, Queues, Payment System at Scale |
| 5 | 05-coding-challenges | Autocomplete, Fuzzy Search, Deep Clone, Flatten, LRU Cache |
Revision Checklist ​
Before LLD Round ​
- [ ] Review design patterns — know when to apply each one
- [ ] Practice Digital Wallet and In-Memory DB problems end-to-end
- [ ] Review SOLID principles → glomopay-prep/notes/03-solid-principles
- [ ] Brush up on JS fundamentals — closures,
this, polyfills
Before HLD Round ​
- [ ] Review CAP theorem — know why payments must be CP
- [ ] Practice Payment System at Scale design end-to-end
- [ ] Know caching strategies and when to use each
- [ ] Review ACID, isolation levels, and locking strategies
Cross-References (Already Covered Elsewhere) ​
| Topic | Where |
|---|---|
| React internals, hooks, fiber | Frontend Concepts 01 |
| State management patterns | Glomopay 02 |
| SOLID principles in React | Glomopay 03 |
| Unit testing patterns | Glomopay 04 |
| Frontend performance | Glomopay 05 |
| Networking & caching (HTTP/3, CORS) | Frontend Concepts 08 |
| Security (CSRF, XSS, CSP) | Frontend Concepts 09 |