I applied for this position in Portugal. The interview process comprised three stages.

The first stage consisted of a typical HR interview. I was contacted via telephone and successfully passed to the next stage. The HR representative was very helpful and provided hints about the upcoming challenge.

The second stage involved live coding. The task was to program the "friend of friends" algorithm in Python, describe the solution, and identify edge cases. I performed well, and the interviewer even decided to ask an additional SQL question since we had time left, which typically doesn't happen. However, the SQL question was poorly structured and required a very specific answer involving the INTERSECT operator, which is not available in all SQL languages and, in my opinion, does not effectively assess knowledge.

After TWO MONTHS (!!!) without any communication, despite my attempts to get an update, I was finally informed that I had passed to the next stage. However, due to my SQL result, they wanted to downgrade the position to a mid-level role. Given their justification, I found this decision quite unreasonable but agreed to proceed. I then scheduled the next two interviews: one focused on a machine learning case study and another about my experience.

The HR representative informed me that I would be interviewed by specific individuals with certain nationalities, but on the day of the interviews, the interviewers were completely different. Although this was not a problem for me, the interviews themselves were disappointing. In the case study interview, the interviewer struggled to speak English properly and conducted the session very poorly. The interview about my projects was equally unsatisfactory; they started the interview by asking about a difficulty I faced at work and how I dealt with it, but they lacked knowledge about my projects and didn't ask for any context.

At the end of the last interview, I inquired about the timeline for a response since I had other opportunities in progress. They assured me I would hear back within a week. However, after ONE AND AN HALF MONTHS (!!!), they sent a message saying they had chosen another candidate, without providing any feedback.

Despite the people being nice, I felt very disrespected and relieved not to be accepted, as such experiences indicate how disorganized and unprofessional the company may be.

What is the difference between train and test? What's the purpose of validation? and other basic ML questions. The case study was about a recommendation system.