Upon joining the meeting, I met with a friendly staff engineer. He asked me for an overview of my background and then immediately jumped into a HackerRank live coding exercise.

The coding exercise itself, like many already mentioned, is to implement a MultiMap data structure, along with some extension methods. I felt I did well until I got to the intersect method. In my opinion, this coding exercise is flawed because:

• The requirements are unclear; the provided visual diagram describes intersect differently than they expect you to implement it.
• The interface to the MultiMap class they ask you to implement makes it very unintuitive to use in an extension method.

Because I tripped up on one extension method, I was not given an offer, despite having performed well the first hour or so of the interview. They didn't even bother getting to know me or ask about my experience, really. In the future, I am going to start declining interviews at companies that do these LeetCode / HackerRank challenges. They prove absolutely nothing about what I can do as an engineer, especially in a Principal role. It's no wonder that they have many negative reviews by people currently working there.

Implement a MultiMap data structure.

Implement extension methods for the MultiMap, such as UnionWith, ExceptWith, IntersectWith, etc.