[istvan__]

I used to work for Amazon, and made it all the way through the Google loops once and I can tell you that you are better than the most of the candidates already, because you made it to the second or third last round.

Applying for positions in these companies comes with hard interview loops and you need to know everything about the stack your code is running on (mostly operating systems and networking). this is true for almost any role there (usually the engineering field is divided: systems, network, software and security engineering. i am not sure what sort of role you were going for but i guess software engineering. those positions also require that you are familiar with extreme scale and you are knowledgable about the usual SDE topics like data structures and algorithms. it is hard to do all of these at once at the level that you are in the top 5% who gets hired.

if you are serious about it, most of the questions and answers are leaked out to the internet so you can just google them and try to understand the problem, study it more if you are not sure (ask stackoverflow etc.) and you can pass the interview the next time (~18 months from now). next time you are going to be more prepared and potentially similar questions going to come up.