I didn't pass further than the first stage, which was the live coding session. The task was pretty simple: design a URL shortener class in pure Java, without any additional libraries or frameworks. There were additional requirements that I had to clarify. I overcomplicated the solution too much and didn't use the correct concurrency and other primitives here and there. The next day, they emailed me detailed feedback highlighting all the shortcomings of my performance! The interviewer, an engineer, was nice throughout the process and gave hints from time to time. I have nothing to complain about.

Design a very simple URL shortener in Java.

In-memory storage is fine, up to 100 URLs. It should have only two methods: shorten and get/unshorten.

The implementation needs to be thread-safe.

This was preferably done in TDD style, but I wasn't following it strictly, and there was nothing on it in the feedback afterwards.

Afterwards, there was a small discussion on how to improve the design, whether it's thread-safe, about the test cases, and so on.