Amazon.com Software Design Engineer Interview

Interview Details – 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.