EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 64: 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 64 of 150 in Extreme Sudoku 2
Difficulty
Expert 6 (expert and beyond), from the middle third of the book
Key technique
ALS-XZ
Hard steps
23 of 46 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: ALS-XZ

Two almost-locked sets (n cells with n+1 candidates) share a restricted digit X. Then a digit Z common to both must be in one of them, so cells seeing all of its copies cannot be Z.

Other advanced and expert techniques in this solve: WXYZ-Wing (×3), Finned Fish (×2), Nice Loops/AICs (×2), W-Wing (×2), XY-Chain (×2), XYZ-Wing (×2), 2-String Kite, Empty Rectangle, Sue de Coq, X-Wing/Swordfish, 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 (23)
  1. Step 3 · Finned Fish expert
    Rules out 3 from R6C7.
  2. Step 6 · XY-Chain expert
    Rules out 6 from R1C5.
  3. Step 8 · WXYZ-Wing expert
    Rules out 7 from R8C5.
  4. Step 9 · WXYZ-Wing expert
    Rules out 3 from R5C9.
  5. Step 10 · ALS-XZ expert
    Rules out 1 from R1C2.
  6. Step 11 · ALS-XZ expert
    Rules out 9 from R3C2.
  7. Step 12 · ALS-XZ expert
    Rules out 8 from R1C5, R2C2.
  8. Step 15 · XY-Wing advanced
    Rules out 6 from R4C4, R6C4.
  9. Step 19 · Empty Rectangle advanced
    Rules out 6 from R8C1.
  10. Step 20 · Sue de Coq expert
    Rules out 6 from R5C5; 7 from R5C5; 8 from R8C6.
  11. Step 21 · X-Wing/Swordfish advanced
    Rules out 7 from R1C1, R1C2, R1C3, R1C9 and 2 more.
  12. Step 22 · 2-String Kite advanced
    Rules out 7 from R4C9.
  13. Step 24 · XY-Chain expert
    Rules out 6 from R4C6.
  14. Step 25 · ALS-XZ expert
    Rules out 9 from R1C2.
  15. Step 27 · ALS-XZ expert
    Rules out 7 from R3C9.
  16. Step 28 · W-Wing advanced
    Rules out 9 from R3C3.
  17. Step 32 · Finned Fish expert
    Rules out 8 from R5C1.
  18. Step 33 · WXYZ-Wing expert
    Rules out 1 from R5C2.
  19. Step 34 · Nice Loops/AICs expert
    Rules out 7 from R5C2.
  20. Step 35 · Nice Loops/AICs expert
    Rules out 1 from R7C3.
  21. Step 36 · XYZ-Wing advanced
    Rules out 8 from R7C1, R7C2.
  22. Step 37 · XYZ-Wing advanced
    Rules out 1 from R5C1.
  23. Step 42 · W-Wing advanced
    Rules out 7 from R5C1.

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.