Here ( http://files.getdropbox.com/u/196807/peaktraffic.tgz ) is a proof of concept of HashFold that I used for my solution for the facebook puzzle ( http://www.facebook.com/careers/puzzles.php?puzzle_id=8 ).

It's written in python. You can run it with './peaktraffic input'. It has 5 different use cases for HashFold: a counter, two different filters, an adjacency list builder, and a cluster finder. The README explains the solution, but does so in terms of MapReduce.

This code wasn't written with the intent of public consumption, so take it as you may.

Any questions, let me know.