I got a LinkedIn message from a recruiter saying that they liked my profile and if I was open to new opportunities. I had one technical phone screen with one of their directors and then moved to an on-site where I had five rounds. One of the interviewers did not show up, due to which the recruiter spent time with me for the whole hour.

Reverse a singly linked list.

High-level questions on multi-threading. Given a list of integers, construct a string in JSON format using basic string operations.

1. Write a Singly LinkedList data structure. How to determine if there is a loop in it.
2. Design a min heap.
3. Write a function to determine if a number is an Armstrong number or not.

You are given a service that can take a maximum of 1 billion requests. If you exceed that count, you will be billed. How do you design a system such that you ensure you don't exceed the above max request cap?