Will Shortz Presents Extreme Sudoku: 100 Challenging Puzzles : So you think you're tough enough? This collection of 100 puzzles was created for only bravest sudoku solvers. Many may attempt to master them but only the sharpest minds will succeed. So put your sudoku skills to the ultimate test and see if you're tough enough for these dangerously devious puzzles. But if you find yourself pulling out your hair in frustration, don't say we didn't warn you.