Meta Research Scientist interview questions

One coding round was followed by another round of 2 coding interviews, one research interview, one systems design interview. They did some background check after the first round. Interviews went pretty well but got a reject.

I interviewed with the neuromotor interfaces team. The overall experience was pleasant and speedy. I first spoke to a recruiter and then did a full loop interview across 2 days (1 technical, 1 design, 1 behavioral, 1 presentation, and 2 more 1:1 interviews). For the presentation, I spoke about my work in academia (no different than your standard conference/job talk). The technical was very difficult. The task was to take a physiological signal, and implement K-means clustering from scratch to try to separate the parts of the signal that derived from different hand movements. You were not explicitly told to use K-means, just some "clustering" method (but K means is the way to go).