Amazon Software Development Engineer interview questions

I got in contact with a recruiter through a friend, and they were going to come to my country to do some interviews. After a first contact email they sent me a url to make an offline telematic interview, and after it I went to the onsite interviews, 5 in total. A couple of weeks after the onsite interviews I got the offer.

Applied through Amazon website. A week later HR contacted to set up a 1 hour phone interview. nterviewer asked to tell about my favorite course project and about my Co-Op Exp. Later asked to write a code in any interested language about how to find two numbers in an array whose sum is equal to a given number. Asked how I can improve it and what its Big O, is it going to compile