Amazon Software Development Engineer interview questions

Recently went through a really long interview process with Amazon which ended in no offer. The process included 3 phone interviews and as per me, I did well in them. I may have taken a little long on some common (still tricky questions) as I haven't looked at them before but in the end I did manage to come up with a solution on my own with some hints from the interviewer. Apart from this, I really can't see any other issue as most other questions I already knew solutions for. I was really hoping for an onsite interview opportunity but instead got a reject. I know amazon have some high bars for their positions but from this process, I really can't make out where I fell short. Anyway will try again in future.