Extreme Killer Sudoku 1, puzzle 13: 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), Coloring/Multi-coloring, 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 (7)
- Step 13 · Multi-Sector Locking advanced
Rules out 3 from R2C7, R3C7. - Step 14 · Forcing Chains expert
Rules out 2 from R2C2. - Step 55 · Multi-Sector Locking advanced
Rules out 2 from R7C4, R8C4. - Step 56 · Advanced Innies (3+ sectors) advanced
Rules out 1 from R4C2; 4 from R4C5; 5 from R4C5. - Step 59 · Remote Pairs expert
Rules out 1 from R7C9; 2 from R7C9. - Step 60 · Coloring/Multi-coloring expert
Rules out 8 from R8C8. - Step 63 · Multi-Sector Locking advanced
Rules out 1 from R2C7, R3C6, R4C8, R5C7 and 1 more.
The book
No starting digits at all: just cages and their totals. Sudoku rules, plus arithmetic, plus a lot of nerve.
150 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 Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.