Three phone calls comprised the initial stage. The first call focused on reviewing my resume. The second was purely mathematical, and the third was data structure-related.

The whole process felt extremely mechanical, as if I were speaking to machines rather than people, with barely any interaction from the interviewers. Each interviewer asked me to introduce myself, but there were no follow-up questions or discussions.

The interviewers simply pulled several brain teasers, math, or data structure questions from a pool and assessed my ability to answer them. One technical question took me only a few seconds to solve, but the interviewer suspected I had encountered the same test before, consequently doubting my integrity and capability.

I never fully understood the interviewers' objectives throughout the process.

Heap insertion complexity. Pop complexity.