See the first post in The Pragmatic Programmer 20th Anniversary Edition series for an introduction. The first two challenges recommend some (excellent) books to the reader, however do not provide a specific challenge for me to write about here. I shall, therefore, begin with the third challenge. Challenge 3 In the first exercise that follows we look at sorting arrays of long integers. What is the impact if the keys are more complex, and the overhead of key comparison is high?