Amazon Software Development Engineer interview questions

I was contacted by an Amazon recruiter who noticed my resume on monster. I had one phone interview of about 90mins and was then asked to come to Seattle. I was apparently interviewing for 2 position so I met 2 hiring managers and about 2 technical people from each of their teams, 6 interviews in all. The technical interviews were nothing special, the standard questions listed here and a couple of curve balls which were really interesting and I cannot disclose them since they were sort of closely related to what they do and thus it would go against my non-disclosure agreement. They treat you really well and make you feel comfortable except when they keep challenging your answer to see if you break :)

First round was online coding +apti. Aptitude was kind of moderately difficult and the coding questions were pretty simple. But you must be aware of using libraries in any language so that you don't have to code all of it. For example, my question required sorting and I was coding in C. I had to switch to Java so that I could use Collections.sort(). Couple of weeks past, I got a mail for telephonic interview which was primarily based on my CV. My skills and projects were asked. Apart from that some basic binary tree coding problems were asked. Next, I was invited for on-site interview where I went for rounds after rounds. Until the third round I could see people walking out. For the fourth and the final round, only 5 out of initial 50 candidates remained.