Extreme Killer Sudoku 1, puzzle 131: 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: Remote Pairs
A chain of cells that all hold the same pair alternates between the two digits. Cells that see both ends of an odd-length link cannot hold either digit.
Other advanced and expert techniques in this solve: Advanced Innies (3+ sectors) (×2), Multi-Sector Locking (×2), Forcing Chains, Skyscraper.
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 25 · Multi-Sector Locking advanced
Rules out 8 from R5C3; 1 from R5C6. - Step 26 · Advanced Innies (3+ sectors) advanced
Places 9 in R8C5 and rules out 9 from R4C5, R5C5, R6C3, R6C5 and 7 more; 4 from R5C5; 6 from R5C8, R6C5. - Step 33 · Multi-Sector Locking advanced
Rules out 1 from R4C2. - Step 34 · Advanced Innies (3+ sectors) advanced
Rules out 9 from R5C3, R5C4. - Step 37 · Remote Pairs expert
Rules out 5 from R4C2; 1 from R5C2, R6C2. - Step 51 · Forcing Chains expert
Rules out 8 from R1C7. - Step 54 · Skyscraper advanced
Rules out 9 from R6C8.
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.