EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 69: 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 69 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
22 of 42 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: ALS-XZ (×3), XY-Chain (×3), 2-String Kite (×2), Finned Fish (×2), WXYZ-Wing (×2), Cell Forcing Chains, Empty Rectangle, Sue de Coq, 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 (22)
  1. Step 5 · 2-String Kite advanced
    Rules out 2 from R8C5.
  2. Step 6 · WXYZ-Wing expert
    Rules out 3 from R8C8.
  3. Step 8 · 2-String Kite advanced
    Rules out 3 from R3C6.
  4. Step 9 · ALS-XZ expert
    Rules out 6 from R3C1.
  5. Step 10 · ALS-XZ expert
    Rules out 4 from R1C5, R2C5, R6C5.
  6. Step 11 · Nice Loops/AICs expert
    Rules out 4 from R4C4.
  7. Step 12 · Nice Loops/AICs expert
    Rules out 8 from R4C2.
  8. Step 14 · WXYZ-Wing expert
    Rules out 6 from R4C3.
  9. Step 15 · ALS-XZ expert
    Rules out 1 from R6C1.
  10. Step 18 · Finned Fish expert
    Rules out 4 from R3C6.
  11. Step 19 · Nice Loops/AICs expert
    Rules out 7 from R5C8.
  12. Step 20 · Empty Rectangle advanced
    Rules out 7 from R2C5.
  13. Step 22 · XY-Chain expert
    Rules out 3 from R3C1.
  14. Step 25 · Nice Loops/AICs expert
    Rules out 1 from R7C9.
  15. Step 26 · Nice Loops/AICs expert
    Rules out 1 from R8C6.
  16. Step 27 · Nice Loops/AICs expert
    Rules out 2 from R8C6.
  17. Step 28 · Cell Forcing Chains expert
    Rules out 6 from R1C8.
  18. Step 32 · XY-Wing advanced
    Rules out 6 from R3C6.
  19. Step 33 · XY-Chain expert
    Rules out 6 from R7C1, R9C8.
  20. Step 35 · Sue de Coq expert
    Rules out 7 from R2C6; 2 from R6C6.
  21. Step 36 · Finned Fish expert
    Rules out 2 from R7C4.
  22. Step 37 · XY-Chain expert
    Rules out 2 from R8C9.

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.