Extreme Killer Sudoku 1, puzzle 47: 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: Advanced Innies (3+ sectors), Empty Rectangle, Remote Pairs, Skyscraper, WXYZ-Wing, XY-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 12 · Advanced Innies (3+ sectors) advanced
Places 7 in R1C4 and rules out 7 from R1C1, R1C2, R1C3, R1C5 and 11 more; 1 from R1C5, R2C5; 4 from R1C5, R2C5, R6C4, R7C4. - Step 16 · Empty Rectangle advanced
Rules out 1 from R5C1. - Step 17 · Forcing Chains expert
Rules out 3 from R3C5. - Step 58 · WXYZ-Wing advanced
Rules out 5 from R7C2, R9C2. - Step 59 · Skyscraper advanced
Rules out 4 from R5C3, R6C8. - Step 60 · Remote Pairs expert
Rules out 3 from R6C2. - Step 62 · XY-Wing advanced
Rules out 5 from R9C5.
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.