Amazon Sr Software Engineer interview questions

Passed Phone Screen since they basically asked OOP ("What is encapsulation?") and Algorithms ("Name an O(n log n) Sort")-kind of questions. They love Bucket Sort, so understand it. Breezed right through. I took time off my current job and flew to Seattle. Got in late on puddle jumpers. The job I was interviewing for had advertised they wanted J2EE, Oracle DB's, XML, standard stuff for a Senior Java guy. However, I was asked about none of that. Instead we emarked on a masturbatory exercise whereby developers one after another propsed what Einstein called "Gedanken Experiments", all of which had to be coded by hand on a whiteboard resulting in compilable code. You are allowed to ask questions of the interviewer and have 60 mins to solve. Here are my questions: 1.) "Given an NxM matrix, with some cells black and some cells white, code an algorithm to find all the black cells." 2.) (This one was from one of the senior developers, an older gentlemen who had been pretty much since the founding). "A road has a traffic counter on it and results in an array of durations since the sampling began. Code and algorithm to find out how many cars have passed, keeping in mind that there may be 18 wheelers, cars towing trailers, pickup trucks and passenger vehicles" 3.) "Given two arrays of floats, not necessarily of the same size, write an algorithm to merge them in ascending order." This was the only one I got completed and correct. 4.) "Given a log file spanning multiple days, and given a page transition A -> B -> C, find all the unique users who made this page transition in the logs" Needless to say, I spent a great deal of time preparing, reading Bertrand's Object Oriented Software Construction and Lafore's "Data Structures and Algorithms in Java". It didn't matter. Could have went in cold and done almost as well. The people were pleasant, but the experience wasn't good.