The interview process consisted of three stages:

1. Phone interview: This stage included one complex system design problem, two coding problems, and two to three specific questions about Python.

2. Second phone interview: This interview featured three coding problems.

3. On-site interview: This involved five sessions, each with one to two interviewers. The first two sessions focused on one coding and one system design problem each. The third session was dedicated to a system design problem. The fourth session assessed background and personality. The fifth session was with HR.

I initially thought I would get the job, especially after meeting the HR staff. However, in the end, I didn't receive an offer. Reflecting on the experience, I now believe the outcome was fair, as I didn't provide entirely satisfying answers in the first session. Securing a senior position appears to be quite challenging, requiring nearly perfect responses.

Data structures and algorithms.