I was failing interviews too until I picked up an undergrad CS algorithms book and read through the first few chapters on data structures and theory. Then I signed up for LeetCode premium. After a couple months of reading and practicing, I was getting an offer from every place I interviewed at. Now I’m at one of those big name software companies, and if I’m ever asked to interview a candidate—well, I don’t know what I’ll do. Maybe something with a binary search tree. I’ve literally never had to use that in 8 years of development. :)