After a few calls talking about my CV and the company, as well as the projects, I was invited to take a test.

It was an online test, live coding on the HackerRank platform. It gives you only 1.5 hours to complete 3 tasks. The platform compiles incredibly slowly, so don't make my mistake: code in your IDE and then copy-paste.

There is just too little time, so if you don't type quickly while thinking, then this is not for you.

Sort an array in a way that frequency comes first.

For example, if you have 2 3 2 1 4 5 1, you need to return 3 4 5 1 1 2 2.

This is because 3, 4, and 5 appear only once, then 1 appears twice, and 2 appears twice.

You are given an array of numbers and need to find pairs which have the lowest difference between them. Return those pairs sorted by the first and then the second number.

For example, given 1 2 4 6 5, you should return 1 2, 6 5.