Amazon Intern Software Engineer interview questions

I was contacted by a recruiter after I handed in my resume in the career fair. I had two 45 min on campus interviews, both were technical, but not very hard. Asked about the 2Sum problem and how to extract the smallest 100 elements from an integer stream. The whole interviews went very well, and the second interviewer was satisfied by my quick solutions. But still don't get an offer. After three days, I got a rejection.

Very professional. Consists of two rounds. 1st round simple. 2nd round a little bit more. Questions: 1) 2nd largest number in an array 2) no:1s in Binary 3) Loops in a singly linked list 4) Hex to decimal 5) Lot of Oops questions 6) Math based 7) Regular expressions