It was a phone interview, the very first round. It consisted of one technical question where you had to describe how you would approach it in the most efficient way and then implement it.

The interviewer called on time. He was very polite, helpful, and friendly.

First, he asked me the most general question: "Tell me about yourself." Then, he discussed some things from my resume.

After that, he moved to the technical question.

Technical Question:

This question is based on an e-commerce setup. There are n order receiving servers that receive orders from customers. There is one other server that fetches orders from these servers and processes them in sequence.

n order receiving servers (each server has m orders):

A: 1, 3, 6, ... B: 2, 5, 7, 9, ... C: 4, 8, 10, ... ... ... ... n

There is no collision when order receiving servers are receiving orders, and the orders are queued up on these servers.

The Order Processing server needs to process these orders in order. This means the server will process order 1 from server A, then order 2 from server B, then order 3 from server A, and so on.

How can the Order Processing server achieve this in the most efficient way? Also, implement the setup.