I had an interview few days back for E5/E4 Facebook London.

Questions asked:

1. https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/
2. https://leetcode.com/problems/leftmost-column-with-at-least-a-one/

I solved both the questions optimally and finished the interview in around 25-30 mins. Interview went quite well except 1 small bug which I was able to fix it after the interviewer pointed it out.

Received a call from recruiter that interview feedback is very positive but sadly there is no headcount left for mid-level engineers as of now. She will get back in few months after there is a headcount available.

Thinking if that's a polite way to reject!