Amazon Software Development Engineer interview questions

Contacted through email by recruiter for recent college graduates. Called for onsite interview. There were approx 15 candidates called for that day all expenses paid trip to Seattle. First one hour discussions, all interviewers mingled with us over lunch giving opportunity to ask various questions about their exp in amazon and work they do etc.. then 4 rounds of 1-1 inteview 45 min each with standard algorithm/problem questions. Interviewers were very nice and friendly and knew what they are looking for. Overall, a very good experience.

I first applied to their career website. Then, 3 phone interviews followed. Each was about one hour long and one month apart. The interviewer would state an algorithm problem and all the questions would be based on this problem. It was possible to solve the problems with many approaches, but only the most optimized one will be accepted by the interviewer. I know nothing about finding talented people, so maybe this is a good way. But, I still felt it's a bit unfair that you are given less than 10 minutes to give the most optimal answer. The interviews themselves were alright, but the process was not pleasant. After the initial inquiry, HR sent me an email to request for the first interview. I replied and waited 2 weeks for the HR to schedule me the interview time. I did fine in the first interview. After another week, HR sent me a request for the second interview and it took another week for her to schedule it. So 1.5 months already passed since I applied. I did alright in the second interview. And the same process for the HR, waited 2 weeks for her to schedule me the 3rd interview, which she scheduled on Black Friday. I sent her an email to confirm the unusual time, but she did not reply. As expected, the interviewer was a no call. A few days later, HR apologized saying the interviewer had an emergency. Anyways, 3rd interview was rescheduled, but I did not do well. By the time I got the rejection email from them, 3 months had passed since I entered my application. One of the interviewer was proud of his profitable company. He said the engineers in Amazon are solving real world problems, implying the rest of us are not?