The interviewer told me to describe one interesting project that I have worked on and discuss about its challenges, including performance or big data aspects. He then asked one technical question: Assume you have a cartesian plane and a set of N points (x, y) from which you want to find the K closest points to the center (0,0). How does the solution change depending on the value of N and K with respect to one another? You would have needed to describe specific data structures and algorithms.