While it is very impressive that this book was written by a high-school student, there are many errors in the examples, sample questions and answers. For instance: On figure 9.7, page 268, the figure atempts to illustrate how Mergesort works but while text says the result is sorted, the list in the figure remains unchanged. Another example -- there are at least two errors in the code for chapter 9 question 21 ("for" loop of j should start at i instead of 1 and that "for" loop never swaps the very last element). And one more (although there are many): The Answer Explanations for chapter 9, questions 22 is an answer for another question.
Again, I comment the author for his efforts and kind heart. (He nobly states early on that he hopes to provide free copies of the book to anyone who can't afford it.) However, if you need to use this book to prepare for the AP Test, you are better off with Barrons. (I purchased both for my twin sons and we wound up purchasing a second copy of Barrons)