Extreme Killer Sudoku 2, puzzle 73: 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: Advanced Innies (3+ sectors) (×3), Forcing Chains, Multi-Sector Locking.
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 14 · Multi-Sector Locking advanced
Rules out 9 from R1C4, R9C5, R9C6; 8 from R9C5, R9C6, R9C7; 1 from R9C7. - Step 15 · Advanced Innies (3+ sectors) advanced
Rules out 3 from R9C5; 4 from R9C5; 5 from R9C5. - Step 17 · Coloring/Multi-coloring expert
Rules out 1 from R6C3, R7C2. - Step 30 · Advanced Innies (3+ sectors) advanced
Rules out 4 from R9C1, R9C2; 5 from R9C1, R9C2, R9C3; 7 from R9C1, R9C3. - Step 63 · Advanced Innies (3+ sectors) advanced
Rules out 8 from R1C4; 7 from R6C4. - Step 64 · Forcing Chains expert
Rules out 6 from R1C1.
The book
Volume two: 150 new killers, none repeated from book 1. 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 Sudoku 3 · Extreme Killer Sudoku 3.