Free sample from Extreme Sudoku 1: step-by-step solution
Print the puzzle first (PDF, A4 or US Letter), then come back and step through the solution, or skip to the hard parts.
Blue digits are placed by the walkthrough. Red strike-through marks a candidate being ruled out. Cells are named by row and column: R3C5 is row 3, column 5. Arrow keys step too.
The key technique: Nice Loops/AICs
An alternating chain of strong and weak links. Whichever end is true, the conclusion holds, so the digit at the marked cell is ruled out.
Every move above the basics is explained on the sudoku techniques page. The book's own 150 puzzles each have a page like this one: all Extreme Sudoku 1 solutions.
The book
Classic 9×9 sudoku with the warm-up taken out. Every grid sits at the top of the expert range or beyond it, and the book ramps from hard to brutal.
Try a free sample puzzle (PDF) · prints on A4 or US Letter