Hi fellows

I recently attented the interview for onebyzero.ai

they concentrated on hld and dsa

hld question :
Design a face book page i.e user can create a page and follower can comment on post.

Since it was first hld interview i didnt performed. But interviewer understand it well and he said we can skip but i told i will try, obviously interviewer was not satisfited with solution.

Later we moved to dsa and question is simple
need to find largest substring with non repeating character. interviewr said code should pass the all testcase and i did it in a single go.

final verdict: not selected (poor in hld).

Also can i get suggestion where to learn hld and multithreading