The Huge Killer Sudoku Book: 2nd edition 2nd edition

This book has 250 of the popular Killer Sudoku puzzles, ranging from easy to very challenging. There are five categories: "Warmup" (with 25 puzzles), "Easy" (50), "Medium" (50), "Tricky" (50), and "Difficult" (75) (so no puzzle is actually impossible :-).

Solving a Killer Sudoku takes a combination of Sudoku-style logic reasoning and basic math skills, making it a much more interesting puzzle. The puzzles are by the author of the popular Calcudoku puzzle books. Solve both Calcudoku and Killer Sudoku puzzles online at calcudoku.org and score points! You can even submit solutions for the difficult puzzles in this book, and score points for each correct solution.

This is the 2nd edition which has the solutions of all puzzles in the back (in other words, it is identical to the 1st edition + all solutions).

To get a sense of the difficulty level of the puzzles in this book, go to killersudoku.com (which has difficult puzzles on Friday, Saturday, and Sunday).