The Number Addict's Book of Hard to Extreme Sudoku 200+ Challenging Sudoku Puzzles

Stimulate your mind with this book of hard to extreme Sudoku puzzles. If you've only progressed to this level, don't get frustrated if it takes you a minimum of an hour to complete a puzzle. You are just getting started. Your mind will soon adapt to the level of difficulty if you continue to work on more puzzles everyday. How many puzzles can you complete today?