I've only been through online coding interviews. Yet, since they (quote) "could not see some signals," I had been put through two of them.

The key "signals" they were looking for were code testing and extreme performance; they were expecting me to solve more than one problem during those 45 minutes.

Both interview problems were something you can consider medium to hard problems on LeetCode.

The second interview was weird, to say the least. In the beginning, the interviewer said we would not run the code, so I thought the best testing I could do was explaining how my algorithm would behave at each step depending on the input. I came up with a solution and a number of edge cases, which I went through verbally, explaining how my algorithm would work in those scenarios. Immediately after I was done, the interviewer asked me to go through the solution and explain how it would work. That felt confusing enough (I had just done exactly that, which I mentioned), but I still went through it again. The feedback I received later stated that I did not do any testing, which was ridiculous.

I communicated this to the recruiter, and she said she would get a more senior member of the team to provide feedback on my interview results. She kept promising to come back with feedback in a week or two, over and over again. This stretched for more than three months. The process was very unprofessional and badly organized, with ridiculously meaningless interviews and feedback.

Implement pattern matching on a large dictionary.