Amazon Software Development Engineer interview questions

Online exam followed by 4 45 min B2B on-site interviews. Questions were challenging. Interview went well. Got a reply in a week saying that they would not be extending an offer. Very surprised to be honest. Never seen a company be so irregular with their interview process and offers. Hope the top management takes note and improves on it. Don't see them competing with the other top companies if their hiring stays so erratic.