Paytm IOS Developer interview questions

Paytm HR contacted me through call after visiting my profile on LinkedIn. They were looking for 2-3 experienced iOS developer. There were 4 rounds in total. Whole process took less than two weeks. In first round, I was asked two coding problems and basic swift questions. Coding problems were of easy difficulty. This was an easy round. HR was very swift and declared the result on the same day only. Second round was most interesting round of all. It involved discussion over architecture patterns and design patterns. We literally fought over how would I manage caching in app. Interviewer was very understanding though and appreciated my reasoning. In third round, one medium level coding problem and some swift related questions were asked. Also I had to explain high level class diagram for a feature. These rounds were of easy to medium difficulty. Fourth round was toughest of all. I was asked to write a class that will replicate the caching mechanism. Class should have utility function to get, set and remove cache data for a key, store the data values in file directory and automatically deallocate memory after certain memory threshold is reached. I had mentioned that I know a bit of backend too, so was asked questions about RESTful APIs and how do I develop APIs. Interviewer also asked me about RabbitMQ and load balancers, what all features I've developed in app end to end and explain any one in detail.