Extreme Killer Sudoku 3, puzzle 15: 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), Coloring/Multi-coloring, Empty Rectangle, Forcing Chains, Multi-Sector Locking, XY-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 11 · Empty Rectangle advanced
Rules out 1 from R1C7. - Step 13 · Advanced Innies (3+ sectors) advanced
Rules out 1 from R7C4; 2 from R7C4; 3 from R7C4. - Step 22 · Multi-Sector Locking advanced
Rules out 9 from R6C8, R6C9, R7C8. - Step 23 · Remote Pairs expert
Rules out 4 from R4C4. - Step 27 · Coloring/Multi-coloring expert
Rules out 9 from R2C3, R7C2. - Step 28 · Forcing Chains expert
Rules out 8 from R2C5. - Step 63 · XY-Wing advanced
Rules out 8 from R4C8.
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.