EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, 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 2
Difficulty
Expert 6 (expert and beyond), from the middle third of the book
Key technique
Nice Loops/AICs
Hard steps
22 of 52 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), WXYZ-Wing (×2), 2-String Kite, Empty Rectangle, Finned Fish, Skyscraper, Sue de Coq, XY-Chain, XYZ-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 4 · Skyscraper advanced
    Rules out 6 from R2C3, R9C1.
  2. Step 7 · 2-String Kite advanced
    Rules out 5 from R9C5.
  3. Step 8 · Empty Rectangle advanced
    Rules out 3 from R1C1.
  4. Step 9 · Finned Fish expert
    Rules out 1 from R3C9.
  5. Step 10 · ALS-XZ expert
    Rules out 1 from R4C7.
  6. Step 12 · WXYZ-Wing expert
    Rules out 9 from R4C9, R6C9.
  7. Step 13 · ALS-XZ expert
    Rules out 5 from R9C9.
  8. Step 14 · Nice Loops/AICs expert
    Rules out 9 from R1C7.
  9. Step 15 · Nice Loops/AICs expert
    Rules out 1 from R3C7.
  10. Step 17 · Nice Loops/AICs expert
    Rules out 3 from R2C5.
  11. Step 18 · ALS-XZ expert
    Rules out 5 from R1C4.
  12. Step 20 · Nice Loops/AICs expert
    Rules out 9 from R8C5.
  13. Step 21 · Nice Loops/AICs expert
    Rules out 9 from R9C8.
  14. Step 23 · Sue de Coq expert
    Rules out 9 from R8C2, R8C3; 5 from R8C3; 6 from R9C9.
  15. Step 26 · Nice Loops/AICs expert
    Rules out 9 from R9C5.
  16. Step 27 · Nice Loops/AICs expert
    Rules out 7 from R4C9.
  17. Step 28 · Nice Loops/AICs expert
    Rules out 9 from R9C9.
  18. Step 34 · Nice Loops/AICs expert
    Rules out 9 from R1C4.
  19. Step 35 · WXYZ-Wing expert
    Rules out 3 from R3C5.
  20. Step 38 · Nice Loops/AICs expert
    Rules out 2 from R1C4.
  21. Step 43 · XY-Chain expert
    Rules out 9 from R8C9.
  22. Step 46 · XYZ-Wing advanced
    Rules out 9 from R1C2.

The book

Volume two: 150 new classic 9×9 grids, none repeated from book 1, 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.

Buy on Amazon US Buy on Amazon UK
Other Amazon stores
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 Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.