I started the process through an external recruiter. The original job description mentioned that it was a remote position, and I explicitly told the recruiter that I was not planning to move to London.

The first step was an interview with the engineer who would be leading the new SRE team being created in Europe. It was an informal talk with some small technical questions, background discussion, and explanations about the new remote team the company wanted to build across Europe (again, I explicitly mentioned that I was supposed to work remotely).

The next step was a technical interview with an engineer from the USA. We used a shared code editor and went over two exercises. The interviewer was very kind and helped me calm down, as I usually get nervous during these "real-time" coding exercises.

Finally, I was told that the next day I was supposed to have a 2-hour videoconference interview, followed by an onsite visit to their office for the final technical interview. This is when things started to go wrong. I didn't receive any interview appointment. After checking with the recruiter who introduced me to Confluent, he told me everything would be delayed due to Thanksgiving week. I waited a week, and they got back to me on a Friday, stating that I would have an interview the following week at their office. They asked me to prepare an architectural design for a SaaS service, similar to their Kafka as a Service product, as we would discuss it for a couple of hours while I was in the London office. There was no mention of plane tickets, so I asked whether I should book them myself. The recruiter's response was a question: "Would you consider moving permanently to London?" I said no, as that was not what I was looking for. I never heard back from them, except for an acknowledgment from the recruiter when I told him I might receive another offer soon from a different company and would need to see some progress from Confluent, or I would not be interested.

There was no rejection email, only silence as an answer.

How would you serialize a binary tree?