The total process of Amazon is really slow....I went through employee referral, OA and final onsite these three phases. Now I will talk about onsite experience: There are four round interviews for onsite interview. Every round begins with some general resume questions such as "tell me about your most proud project/activity" etc. Then the interview is followed by one or two algorithm question: Round one: 1. compare two trees return if they are equal; 2. merge sort(follow up: how about have two large files with each contains a bunch of number) Round two: 1. max subarray sum(follow up: can you do that without array); 2.zigzag travel of a tree Round three:1. given an integer, start from the end put a comma after first three digits, and for the rest, put a comma after every two digits, return final string; 2. I can't remember very clearly about this round, but I do remember it's a dfs or bfs search for a maze with additional constraints such as "each time I can only go forward and turn right" Round four: implement the checkin and checkout interface, I think this problem has been mentioned in previous reviews Generally, Amazon onsite is not hard but I still don't get offer, maybe I performed badly for behavior questions. As for algorithm, it's just about searching, sorting and a little dynamic programming. As for data structure, I heard that they prefer array and string than tree.