PayTM Interview Experience - OnCampus

There was an OA with 2 DSA question 1 SQL question and 5 MCQs. Interview had 2 rounds both technical each of 45-50 mins. Verdict - SELECTED

Interview R1:

Introduction and then I was explicitly told that DSA code won't matter that much, the approach will be the deciding factor for evaluation for that interviewer.

Started with CS Fundamental Questions:

1. Difference bw Process and Thread (independent parts of a process for concurrency and lightweight computation)
2. What is DB Normalisation (Controlling redundancy, integrity constraints)
3. What happens when I type any URL and press enter in Browser (DNS flow).
4. Call by reference and call by value in C (I had a project in C).

I gave big answers for all four questions and went a little more out from topics as well.

Then came the DSA:

1. Linked List Cycle Detection In this I was asked what if slow and fast were not moved by 1 and 2 but by 1 and 3 or by 2 and 4, what will change in that cases - I told that 1 and 3 will work fine but 2 and 4 will create issue sometimes when cycle size is even, I was given time to dry run and think this (I don't think he was convinced).

2. Minimum Coins to make that amount. In this I deliberately started from why greedy solution won't work and we require to try all possibilities. Wrote code for recursion and then memoised it as well told TC and SC for both cases with reasons by drawing a tree showing overlapping subproblems.

Lastly we discussed about why I made these projects and what were the projects about.

Interview R2:

Started with Introduction and about the things that were asked in R1. I had OAuth Implemented in one of my Full Stack projects so he asked the whole flow of like code - short lived - long lived - storage - how refresh happens. Difference between statless and statefull in this particular case, where to store short lived and where long lived.

Then he asked me to design database tables for making a OAuth system like Permission Tables, Token Table, Customer Table. Database choice for these, What are ACID properties, relation is many to many between token and permissions table, also a bit about horizontal and vertical scaling in databases, strong and eventual consistency.

Talked about Saga transaction in distrbuted System and how flow matches in my project and where did I implement that. What are Choreography and Orchestration flows of Saga.

Then about 2nd project it was RAG based search engine I explained BM25, Semantic and Hybrid retrieval pipelines. I was asked about how to give more score to PRO and NON-PRO users.

Another DSA Question at last, Given a sorted array and a target element - find the first and last occurring index for the target element. Simple 2 times binary search implementation.