B Tree related questions, plus probability questions, and a lot of questions related with algorithm& data structure. and also some questions with code optimization. it might be a difficult Challenge if you never touch code optimization with computer architecture.

Early August. Found job posting through HackerNews, emailed them my resume and cover letter. They quickly got back to me. First round was 30-45 minutes of skyping, two programming questions. The first had to do with graph traversal, the second was calculating the sum of Manhattan distances between a certain number of points. I was then asked to optimize it. The second round, a 2-hour coding challenge, was to write a calculator. Mine passed their test cases, but either wasn't good enough or I used poor coding practices because I was rejected.