Extreme Killer Sudoku 1, puzzle 122: 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: 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.
Other advanced and expert techniques in this solve: Multi-Sector Locking (×2), Advanced Innies (3+ sectors), Forcing Chains, Remote Pairs, XYZ-Wing.
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 (7)
- Step 16 · Multi-Sector Locking advanced
Rules out 8 from R3C8. - Step 17 · Advanced Innies (3+ sectors) advanced
Rules out 3 from R1C7, R2C7, R7C6; 4 from R1C7, R2C7, R7C5, R7C6 and 2 more; 7 from R1C7, R2C7. - Step 43 · Multi-Sector Locking advanced
Rules out 1 from R2C1, R3C1, R5C2. - Step 47 · Coloring/Multi-coloring expert
Rules out 6 from R2C3. - Step 49 · Forcing Chains expert
Rules out 5 from R1C7. - Step 55 · XYZ-Wing advanced
Rules out 8 from R1C1. - Step 56 · Remote Pairs expert
Rules out 8 from R2C3.
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.