Amazon Software Development Engineer interview questions

I interviewed with Amazon for a Summer Internship. The process took less than 3 weeks. I had two back-to-back 45 minute phone-interviews scheduled. Within a week I was informed of the decision. The questions were of average difficulty. They were mostly looking for strong Computer Science fundamentals. The first interviewer was interested in details of one of my projects. He then moved on to asking me a few fundamental questions about inheritance. The coding problem involved merging two unsorted strings. The interviewer was also interested in questioning me on how the code would scale if the strings grow to large. The second interview was more grilling, the interviewer gave me a situation where a web server not performing as expected and wanted me to dive deep into deciphering what all could have gone wrong. I was then asked to implement 'toString' Java API.