Amazon Software Design Engineer interview questions

I was contacted by email after visiting the Amazon booth at my university's Career Fair, and a recruiter set up an on-campus interview. My first interviewer was very chill, but was almost plodding in his need for detail. Another peculiar technique was to ask for a solution, and when I gave him one, ask for another and another and another and another, until I was giving less and less efficient solutions. He wanted me to admit that some of the naive solutions would be faster to implement than my initial optimal solutions, and therefore valuable when you want to get a feature out there immediately and scale it up later. Then, he had me code on a piece of paper, and was very picky about syntax. I received a phone call from him about an hour later, congratulating me and setting up three more on-campus interviews for two days later. My second interviewer was also pretty chill. He started out by enthusiastically describing the challenges of optimal shipping. He had me code up a couple problems on the white board, and seemed surprised by my use of bitwise operators. My third interviewer was the most senior. He had me design a chess game, and implement several of the key classes and methods. He also asked me some behavior questions relating to my past experiences with group coding projects. My final interviewer had to have been the bar-raiser. He was a short dude with a very intense stare. As soon as I walked over to his cubicle, he informed me that he "had been listening to [my] last interview through the wall". I was kind of weirded out, but relieved that I hadn't screwed up the last one. The final interviewer asked me some more behavioral questions, and had me code up a LRU cache. I hadn't done that problem before, so it was fun working up to the optimal solution. A week later, I got an email congratulating me and asking to set up a phone call to discuss the offer. They also invited me to Amazon headquarters to stay for three nights, meet all the teams, and hang out in Seattle for the weekend. I haven't decided whether to accept the offer, but I am looking forward to the visit!

Note, this interview process was for a summer internship. The process began with a phone conversation with an HR person. The conversation consisted of gauging my interest in various groups that I could work with at amazon. Later, I went through the first technical phone interview. This lasted about 45 minutes. I was first asked to list which programming languages I had used and how strong I was in each. I was then asked some java specific questions: What is the purpose of the static keyword? What is the difference between a String and a StringBuffer? Then, some object oriented design questions. Then some simple algorithmic questions: Find a common ancestor in a binary tree, find first non-repeated character in a string. All of these questions were answered verbally and the interviewer was satisfied with a general solution. The second technical phone interview lasted about an hour. It began with some discussion of my resume. I was asked questions related to: General operating system details: - Difference between process and thread - What does it mean for a method to be threadsafe - Know what a stack crash is? -> what happens during a function call, how can this be exploited Programming: - Find unique words in text files - Cell phone, phone book, data structure for storing numbers, so that you could type first letter and see what names it matched -> essentially looking for a prefix tree - Have you used makefiles before -> was going to go into a tree description of that - How would you output a tree by level Bit-twiddling - How could you tell if a byte only contained a 1 in the leftmost bit - How could you count the number of ones in a byte Design - Email sender, need to send 100,000000 emails and you have 5 machines how could you do it efficiently These first two interviews felt pretty relaxed. When describing the solution to a problem I would give a quick sketch, saying something like "I would hash a count of each letter" and at this point the interviewer would acknowledge that I was on the right track and just move onto another question without digging for details. In the third technical phone interview consisted of a single programming task. I was asked to code up the solution to a simple problem and email it to the interviewer. This took about 30 minutes, I then described what the code was doing to the interviewer. I did not find the programming question hard, and this last interview felt like more of a formality. At no point did I feel like I had the burden of convincing the interviewer that I was the right candidate. Worth noting, is that I had previously done an internship with Amazon, and this may have influenced how the interviewers were behaving toward me.