Extreme Killer Sudoku 2, puzzle 124: 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) (×2), Forcing Chains, Multi-Sector Locking, Remote Pairs, XYZ-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 · Advanced Innies (3+ sectors) advanced
Places 1 in R3C5 and rules out 1 from R1C5, R1C6, R2C5, R2C6 and 8 more; 3 from R3C6; 4 from R3C6. - Step 38 · Advanced Innies (3+ sectors) advanced
Rules out 1 from R5C6; 3 from R5C6. - Step 56 · XYZ-Wing advanced
Rules out 7 from R7C3. - Step 57 · Multi-Sector Locking advanced
Rules out 2 from R7C1, R7C2. - Step 58 · Coloring/Multi-coloring expert
Rules out 8 from R7C3. - Step 65 · Remote Pairs expert
Rules out 8 from R8C4. - Step 66 · Forcing Chains expert
Rules out 1 from R2C3.
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.