In general this is a mistake of interviewer asking question they would not be able to answer themselves. It is super easy to get this wrong. A problem seems mu

In general this is a mistake of interviewer asking question they would not be able to answer themselves. It is super easy to get this wrong. A problem seems much easier when you know the solution. Also, as interviewer you don't want to make mistake of comparing the candidate's knowledge to your experiences -- the candidate might be completely fine but just happened to have different experience from yours and did not meet the same problems as you. I have a small set of problems which I honed over the years. Some of them are problems which I got when I applied, which makes it easier for me to understand how it is when you are on the other side. Every single problem I have solved in every way I can imagine so that when I interview the candidate I can focus on the other stuff that I care about. I have developed understanding of where the candidates get stuck and for what reasons and how to best provide hints so that I can keep the session productive. When the candidate is stuck for a long time I tend to view this as my failure (nothing is happening == I am not learning anything) unless the candidate is really bad. What I am trying to say is that preparing good problems for coding interview is a hard task and badly prepared problems are probably why so many leetcode interviews are frustrating and inefficient.