Hopper interview questions

I had a series of many interviews with Hopper, I think 5 in total, that did not culminate in an offer. After the first interview I was given a homework problem that I found interesting. Each part of the problem focused on a problem that seemed quite close to real problems they were working on at Hopper. I was bounced around to different departments to find the best 'fit', eventually landing in a remote interview with a VP. I may have made mistakes in one or more answers, as I was not given an offer. Due to the protracted nature of process and the type of 'homework' problems offered, I could not shake a suspicion that they were motivated at least partly by the input we gave, i.e. were using applicants for ideas, essentially consulting. Or maybe I'm just bitter I didn't get the job ;)

Very polite interviewer. I was asked 15-min previous work experience and 45-min technical questions. When a binary tree is given, print out all the Node using recursion and iteration. It was challenging but got an email from them saying I wasn't selected.