Amazon Software Development Engineer interview questions

What algorithm would you use to search a sorted list? What is the complexity of the algorithm? Implement the algorithm in your language of choice.

An integer is represented in binary as a sequence of 0's and 1's. Write a function that returns the number of 1's in the binary representation of a given integer.

Suppose you have a system that keeps track of thousands of users' contact information, including email address. This information is stored in plain text, on disk in a hierarchical directory structure (on a Unix operating system) organized by year, month, and day it was entered in the system. Something bad happens and the system crashes. We want to get the email address of all these users to notify them. How would you parse these directories and files to generate a simple list of email addresses?