The Preface does mention that it is a draft in progress and even asks for feedback.
The author even goes so far as to note that the drawings are copyrighted and he would love to find someone who can help him with originals. Maybe that is someone on HN?
http://www.amazon.com/Think-About-Algorithms-Jeff-Edmonds/dp...
Because of this, I wonder a bit what's the legal status of this .pdf, but maybe I'm overreacting...