Extreme Killer Sudoku 1, puzzle 64: step-by-step solution
Step through the whole solution, or skip to the hard parts. Blue digits are placed by the walkthrough; red strike-through marks a candidate being ruled out.
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: Forcing Chains
Try each candidate of one cell in turn. Every choice leads to the same result, so that result must be true.
Other advanced and expert techniques in this solve: Advanced Innies (3+ sectors) (×2), Empty Rectangle, Remote Pairs.
Every move above the basics is listed on the killer sudoku techniques page, each with a one-sentence explanation and worked examples from the books.
The hard steps, in text (5)
- Step 21 · Empty Rectangle advanced
Rules out 5 from R5C6. - Step 22 · Advanced Innies (3+ sectors) advanced
Rules out 8 from R2C5, R5C5; 7 from R5C5; 9 from R5C5. - Step 23 · Forcing Chains expert
Rules out 9 from R2C1. - Step 59 · Advanced Innies (3+ sectors) advanced
Rules out 6 from R2C5. - Step 60 · Remote Pairs expert
Rules out 1 from R8C6; 7 from R8C6.
The book
No starting digits at all: just cages and their totals. Sudoku rules, plus arithmetic, plus a lot of nerve.
150 puzzles. Expert and beyond. Puzzles by M. J. Bailey. Paperback, 5 × 8 in, 196 pages, £9.99 / $11.99. Every solution in the book carries a QR code to its own walkthrough, so you can check one step without seeing the whole answer.
Try a free sample puzzle (PDF) · prints on A4 or US Letter
More step-by-step solutions: Extreme Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.