I had a phone conversation with the recruiter who told me that the first stage would be an algorithm interview and it would give them an indication of my seniority - red flag 1.

During the phone conversation, I asked about the role and was told it was confidential - red flag 2. It is extremely arrogant and silly to expect people to apply to a role they don’t know about.

I asked about how the algorithm interview would be conducted. I raised my concerns that I don’t mind solving algorithms, but the interviewer needs to give me space to solve the problem at hand and needs to be experienced at interviewing.

Red flag 3, despite my concerns:

Two weeks later, they assigned a junior chap whose first job is at Google to interview me. Despite me solving the problem and improving runtime performance as requested, he nitpicked on my syntax errors and "edge cases" (which I fixed after him implying those during the interview), and I got a rejection.

Extremely frustrating experience. I really don’t think they train their employees properly to conduct a professional interview. I don’t think I will interview there again until they sort out their arrogance.

Writing an algorithm and improving runtime, etc.