Extreme Killer Sudoku 3, puzzle 31: 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: Forcing Chains, Multi-Sector Locking, Remote Pairs, 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 (6)
- Step 16 · Skyscraper advanced
Rules out 3 from R7C3, R9C7. - Step 49 · Multi-Sector Locking advanced
Rules out 1 from R7C4. - Step 51 · Coloring/Multi-coloring expert
Rules out 3 from R3C4. - Step 53 · Forcing Chains expert
Rules out 7 from R1C8. - Step 60 · Remote Pairs expert
Rules out 6 from R5C5; 9 from R5C5. - Step 61 · Coloring/Multi-coloring expert
Rules out 5 from R2C5, R4C6.
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.