EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 68: 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 68 of 150 in Extreme Sudoku 1
Difficulty
Expert 5 (expert and beyond), from the middle third of the book
Key technique
ALS-XZ
Hard steps
27 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: 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: Empty Rectangle (×5), XY-Chain (×5), Nice Loops/AICs (×3), W-Wing (×2), 2-String Kite, Finned Fish, Sue de Coq, X-Wing/Swordfish.

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 of 27)
  1. Step 7 · ALS-XZ expert
    Rules out 2 from R4C3.
  2. Step 8 · ALS-XZ expert
    Rules out 2 from R2C8.
  3. Step 9 · ALS-XZ expert
    Rules out 7 from R6C1.
  4. Step 12 · Empty Rectangle advanced
    Rules out 2 from R4C9.
  5. Step 13 · Sue de Coq expert
    Rules out 3 from R7C7, R8C9, R9C9; 6 from R7C7.
  6. Step 14 · Empty Rectangle advanced
    Rules out 6 from R9C4.
  7. Step 15 · W-Wing advanced
    Rules out 9 from R4C7, R6C7, R8C9.
  8. Step 17 · Empty Rectangle advanced
    Rules out 6 from R7C1.
  9. Step 18 · Empty Rectangle advanced
    Rules out 2 from R8C3.
  10. Step 19 · ALS-XZ expert
    Rules out 6 from R7C8, R8C8.
  11. Step 21 · Nice Loops/AICs expert
    Rules out 2 from R1C3.
  12. Step 22 · 2-String Kite advanced
    Rules out 2 from R4C2.
  13. Step 23 · ALS-XZ expert
    Rules out 2 from R6C4.
  14. Step 25 · ALS-XZ expert
    Rules out 2 from R8C2.
  15. Step 26 · ALS-XZ expert
    Rules out 5 from R4C6.
  16. Step 27 · Nice Loops/AICs expert
    Rules out 8 from R7C4.
  17. Step 29 · Nice Loops/AICs expert
    Rules out 6 from R3C1.
  18. Step 30 · W-Wing advanced
    Rules out 3 from R8C8.
  19. Step 32 · X-Wing/Swordfish advanced
    Rules out 6 from R7C6.
  20. Step 33 · ALS-XZ expert
    Rules out 4 from R7C6.
  21. Step 36 · Empty Rectangle advanced
    Rules out 2 from R3C1.
  22. Step 39 · Finned Fish expert
    Rules out 4 from R8C1.
  23. Step 40 · XY-Chain expert
    Rules out 3 from R2C2, R3C7.
  24. Step 42 · XY-Chain expert
    Rules out 3 from R9C8.

The book

Classic 9×9 sudoku with the warm-up taken out. Every grid sits at the top of the expert range or beyond it, and the book ramps from hard to brutal.

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.

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 Killer Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.