EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 14: 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 14 of 150 in Extreme Sudoku 1
Difficulty
Expert 6 (expert and beyond), from the opening third of the book
Key technique
ALS-XZ
Hard steps
22 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: 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: Nice Loops/AICs (×4), Finned Fish (×2), WXYZ-Wing (×2), XY-Wing (×2), Sue de Coq, X-Wing/Swordfish, XY-Chain.

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 6 · XY-Wing advanced
    Rules out 5 from R7C7, R8C6.
  2. Step 7 · Finned Fish expert
    Rules out 6 from R3C5.
  3. Step 8 · ALS-XZ expert
    Rules out 5 from R9C6.
  4. Step 12 · Finned Fish expert
    Rules out 4 from R6C7.
  5. Step 13 · Sue de Coq expert
    Rules out 8 from R1C7, R1C8, R3C7.
  6. Step 14 · ALS-XZ expert
    Rules out 5 from R8C1.
  7. Step 15 · ALS-XZ expert
    Rules out 1 from R4C3.
  8. Step 16 · Nice Loops/AICs expert
    Rules out 4 from R1C8.
  9. Step 18 · ALS-XZ expert
    Rules out 2 from R6C5.
  10. Step 19 · Nice Loops/AICs expert
    Rules out 6 from R3C7.
  11. Step 21 · ALS-XZ expert
    Rules out 7 from R6C7.
  12. Step 23 · ALS-XZ expert
    Rules out 9 from R4C8.
  13. Step 24 · ALS-XZ expert
    Rules out 1 from R4C8.
  14. Step 26 · Nice Loops/AICs expert
    Rules out 2 from R6C3.
  15. Step 27 · X-Wing/Swordfish advanced
    Rules out 2 from R9C2, R9C6.
  16. Step 30 · WXYZ-Wing expert
    Rules out 3 from R7C3.
  17. Step 31 · ALS-XZ expert
    Rules out 3 from R6C2.
  18. Step 32 · Nice Loops/AICs expert
    Rules out 3 from R6C1.
  19. Step 34 · WXYZ-Wing expert
    Rules out 1 from R5C3.
  20. Step 35 · ALS-XZ expert
    Rules out 1 from R3C5.
  21. Step 39 · XY-Chain expert
    Rules out 3 from R4C4.
  22. Step 44 · XY-Wing advanced
    Rules out 3 from R1C1, R7C2.

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.

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More step-by-step solutions: Extreme Killer Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.