Extreme Killer Sudoku 3, puzzle 121: 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, X-Wing/Swordfish, 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 33 · Advanced Innies (3+ sectors) advanced
Rules out 2 from R5C5; 5 from R5C7. - Step 63 · XYZ-Wing advanced
Rules out 6 from R2C9. - Step 65 · Multi-Sector Locking advanced
Rules out 9 from R2C9. - Step 72 · X-Wing/Swordfish advanced
Rules out 7 from R1C7, R1C8, R8C2, R8C7 and 1 more. - Step 75 · Coloring/Multi-coloring expert
Rules out 6 from R4C7. - Step 79 · Multi-Sector Locking advanced
Rules out 6 from R9C8. - Step 80 · Forcing Chains expert
Rules out 7 from R1C1.
The book
Volume three: 150 new killers, none repeated from books 1 or 2. No starting digits, just cages and their totals, ramping from hard to brutal.
150 new 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 Killer Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Sudoku 3.