EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, 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 2
Difficulty
Expert 5 (expert and beyond), from the opening third of the book
Key technique
ALS-XZ
Hard steps
22 of 50 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: XY-Wing (×6), XY-Chain (×4), Nice Loops/AICs (×2), XYZ-Wing (×2), Sue de Coq, WXYZ-Wing, 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 (22)
  1. Step 4 · XY-Wing advanced
    Rules out 2 from R2C4.
  2. Step 5 · XY-Wing advanced
    Rules out 9 from R2C1, R2C3, R3C5.
  3. Step 8 · XY-Wing advanced
    Rules out 6 from R1C9.
  4. Step 10 · Sue de Coq expert
    Rules out 5 from R1C1, R1C3; 6 from R1C1, R1C4, R1C6; 2 from R2C7.
  5. Step 11 · XY-Wing advanced
    Rules out 9 from R1C6, R2C8.
  6. Step 14 · ALS-XZ expert
    Rules out 9 from R8C9.
  7. Step 15 · ALS-XZ expert
    Rules out 3 from R4C4.
  8. Step 18 · ALS-XZ expert
    Rules out 9 from R6C7.
  9. Step 19 · Nice Loops/AICs expert
    Rules out 4 from R6C8.
  10. Step 20 · Nice Loops/AICs expert
    Rules out 2 from R3C3.
  11. Step 23 · XY-Chain expert
    Rules out 6 from R5C5.
  12. Step 24 · ALS-XZ expert
    Rules out 8 from R4C1.
  13. Step 28 · ALS-XZ expert
    Rules out 3 from R6C6.
  14. Step 30 · WXYZ-Wing expert
    Rules out 9 from R7C7, R7C8.
  15. Step 33 · XY-Wing advanced
    Rules out 5 from R2C1.
  16. Step 34 · XYZ-Wing advanced
    Rules out 3 from R8C7.
  17. Step 35 · XY-Chain expert
    Rules out 5 from R1C7.
  18. Step 36 · XY-Chain expert
    Rules out 9 from R1C8.
  19. Step 41 · X-Wing/Swordfish advanced
    Rules out 6 from R2C1.
  20. Step 42 · XY-Wing advanced
    Rules out 8 from R9C1, R9C3.
  21. Step 44 · XY-Chain expert
    Rules out 7 from R2C1.
  22. Step 46 · XYZ-Wing advanced
    Rules out 7 from R5C3.

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.

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