Free sample from Extreme Killer 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: Coloring/Multi-coloring
Following one digit’s strong links, cells get two colours: one colour is true and the other is false. A cell that sees both colours cannot hold the digit.
Every move above the basics is explained on the killer sudoku techniques page. The book's own 150 puzzles each have a page like this one: all Extreme Killer Sudoku 1 solutions.
The book
No starting digits at all: just cages and their totals. Sudoku rules, plus arithmetic, plus a lot of nerve.
Try a free sample puzzle (PDF) · prints on A4 or US Letter