Extreme Killer Sudoku 3, puzzle 72: 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: Forcing Chains
Try each candidate of one cell in turn. Every choice leads to the same result, so that result must be true.
Other advanced and expert techniques in this solve: Multi-Sector Locking (×3), Advanced Innies (3+ sectors), Remote Pairs.
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 (6)
- Step 11 · Multi-Sector Locking advanced
Rules out 1 from R8C5, R9C3. - Step 19 · Multi-Sector Locking advanced
Rules out 7 from R5C4. - Step 20 · Advanced Innies (3+ sectors) advanced
Rules out 9 from R5C2; 3 from R5C4, R5C5; 4 from R5C4, R5C5. - Step 26 · Forcing Chains expert
Rules out 7 from R5C2. - Step 60 · Multi-Sector Locking advanced
Rules out 2 from R1C7, R2C7; 7 from R1C7, R1C8, R1C9, R2C6 and 1 more. - Step 64 · Remote Pairs expert
Rules out 6 from R2C7, R2C8; 1 from R2C8.
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.