EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 66: 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.

Puzzle
Sudoku, number 66 of 150 in Extreme Sudoku 3
Difficulty
Expert 7 (expert and beyond), from the middle third of the book
Key technique
Nice Loops/AICs
Hard steps
24 of 47 steps need an advanced or expert technique

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: Nice Loops/AICs

An alternating chain of strong and weak links. Whichever end is true, the conclusion holds, so the digit at the marked cell is ruled out.

Other advanced and expert techniques in this solve: 2-String Kite (×2), ALS-XZ (×2), WXYZ-Wing (×2), X-Wing/Swordfish (×2), Cell Forcing Chains, Finned Fish, Skyscraper, Sue de Coq, XY-Chain, XY-Wing.

Every move above the basics is listed on the sudoku techniques page, each with a one-sentence explanation and worked examples from the books.

The hard steps, in text (24)
  1. Step 5 · X-Wing/Swordfish advanced
    Rules out 1 from R3C7, R8C6.
  2. Step 6 · 2-String Kite advanced
    Rules out 5 from R8C4.
  3. Step 8 · 2-String Kite advanced
    Rules out 5 from R2C3.
  4. Step 9 · XY-Chain expert
    Rules out 9 from R2C9.
  5. Step 10 · Sue de Coq expert
    Rules out 3 from R6C3.
  6. Step 11 · ALS-XZ expert
    Rules out 5 from R8C5, R9C3.
  7. Step 14 · ALS-XZ expert
    Rules out 9 from R2C7.
  8. Step 15 · Nice Loops/AICs expert
    Rules out 9 from R4C9.
  9. Step 16 · Finned Fish expert
    Rules out 9 from R1C1.
  10. Step 17 · Nice Loops/AICs expert
    Rules out 3 from R8C8.
  11. Step 19 · Nice Loops/AICs expert
    Rules out 8 from R7C7.
  12. Step 20 · Nice Loops/AICs expert
    Rules out 8 from R7C8.
  13. Step 22 · Nice Loops/AICs expert
    Rules out 9 from R6C7.
  14. Step 23 · Nice Loops/AICs expert
    Rules out 9 from R3C8.
  15. Step 24 · Nice Loops/AICs expert
    Rules out 2 from R2C6.
  16. Step 25 · Cell Forcing Chains expert
    Rules out 8 from R5C9.
  17. Step 28 · WXYZ-Wing expert
    Rules out 8 from R2C6.
  18. Step 29 · Nice Loops/AICs expert
    Rules out 8 from R1C8.
  19. Step 30 · WXYZ-Wing expert
    Rules out 2 from R3C7.
  20. Step 31 · Nice Loops/AICs expert
    Rules out 2 from R1C6.
  21. Step 33 · Nice Loops/AICs expert
    Rules out 6 from R1C3, R3C8.
  22. Step 38 · X-Wing/Swordfish advanced
    Rules out 9 from R1C6.
  23. Step 40 · Skyscraper advanced
    Rules out 7 from R2C7, R3C4.
  24. Step 41 · XY-Wing advanced
    Rules out 7 from R3C8.

The book

Volume three: 150 new classic 9×9 grids, none repeated from books 1 or 2, 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.

On Amazon from 8 Dec About the book

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 Killer Sudoku 2 · Extreme Killer Sudoku 3.