Amazon First Phone Interview

Well I just had the first phone interview and with the question fresh in my mind, here they goes.
1. He asked me about my thesis
2. Then he asked write code for reversing the string
3. Next was finding the no which appeared twice in an integer array having values ranging from 1 to n-1
4. He went on to ask me how can you do a BFS on a tree and then asked me to code it using the data structure of my choice for which I used the Queue, you can implement with anything
5. Then, he asked me to design a class diagram for Deck of cards
6. Then, he asked me to tell him how will you design an online system.

I am so sleepy right now so I didnt included the answers, i ll do this first in the morning , apologies for such a bad post but I wanted to write it out so that I dont miss anything