Extreme Killer Sudoku 1, puzzle 87: 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: Remote Pairs
A chain of cells that all hold the same pair alternates between the two digits. Cells that see both ends of an odd-length link cannot hold either digit.
Other advanced and expert techniques in this solve: Advanced Innies (3+ sectors), Empty Rectangle, 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 (5)
- Step 22 · Empty Rectangle advanced
Rules out 2 from R1C9. - Step 25 · Multi-Sector Locking advanced
Rules out 5 from R4C5, R5C5; 8 from R4C5, R5C5. - Step 26 · Advanced Innies (3+ sectors) advanced
Rules out 4 from R4C1; 6 from R4C5; 9 from R5C5. - Step 30 · Remote Pairs expert
Rules out 6 from R4C6; 9 from R4C6. - Step 61 · Forcing Chains expert
Rules out 6 from R7C1.
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.