Extreme Killer Sudoku 3, puzzle 20: 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), 2-String Kite, Empty Rectangle, Finned Fish, Forcing Chains.
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 12 · Advanced Innies (3+ sectors) advanced
Places 6 in R2C5 and rules out 6 from R1C5, R2C1, R2C2, R2C7 and 3 more; 3 from R2C6, R3C6; 4 from R2C6, R3C6. - Step 30 · Advanced Innies (3+ sectors) advanced
Rules out 4 from R3C7, R4C7; 9 from R5C3. - Step 34 · Remote Pairs expert
Rules out 5 from R4C3; 7 from R4C3. - Step 35 · Forcing Chains expert
Rules out 7 from R2C3. - Step 61 · 2-String Kite advanced
Rules out 8 from R9C2. - Step 62 · Empty Rectangle advanced
Rules out 4 from R2C1. - Step 63 · Finned Fish expert
Rules out 4 from R8C2.
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.