Amazon Software Development Engineer interview questions

Interview with payment team, after 2 phone interviews, Amazon invited me to Vancouver office with 4 interview. From 8am~12PM, there are 4 questions, 2 algorthm/coding questions, 2 OOD questions, the interviewers from different groups

I was called for an onsite day long interview in Seattle. The interview was a group/team coding exercise. In the morning after a tour of the amazon campus in Seattle, we were divided into groups of 3 and given a laptop to work on. You could select an OS and IDE of your preference to work on. We were given a problem which had 3 tasks and each of us had to take on of them. The coding started around 11 in the morning and lasted till 4:30 in the evening. In the duration I had 2 one on one interviews, the 1st one 30 mins into the exercise and the 2nd one an hour before the turning in of our codes. The interviews focused on the approach I had decided on to solve the problems. Which data structure, any optimizations I could think of if I had more time.