Extreme Killer Sudoku 1, puzzle 115: 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: Finned Fish
An X-Wing or Swordfish with one extra candidate (the fin). Cells that are in the fish pattern and also see the fin lose the digit.
Other advanced and expert techniques in this solve: Advanced Innies (3+ sectors) (×2), Forcing Chains, Skyscraper.
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 32 · Skyscraper advanced
Rules out 1 from R2C6, R3C6, R8C4. - Step 34 · Advanced Innies (3+ sectors) advanced
Rules out 2 from R1C6, R1C7; 5 from R1C6, R1C7; 7 from R8C6. - Step 49 · Finned Fish expert
Rules out 7 from R1C9, R2C9. - Step 54 · Forcing Chains expert
Rules out 9 from R1C3. - Step 60 · Advanced Innies (3+ sectors) advanced
Rules out 5 from R5C1.
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.