Amazon Software Developer I interview questions

At the beginning I was contacted by LinkedIn for a Technical Recruiter. She almost immediately set up the first phone interview. Two days after I got a technical phone interview with a really nice guy. He asked me if I knew about the position and He explained me shortly some of the details. After that we started with some programming questions: Determine the number of bits on in a bit array and then how to get the binary number from a decimal number. After that we discussed about how to design a File System using OO and at the end he asked me if I had any question to him. In the second interview the process started different. She asked some question related to my current job, how to deal with estimations and how we solved difficult situations. after that she asked to get the height of a Binary tree and we discuss some test scenarios. I am still waiting for response.

I had 3 telephonic rounds and 4 technical + 1 HR in 1:1. all interviews were pretty good. But didnt get an offer