EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 95: 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 95 of 150 in Extreme Sudoku 1
Difficulty
Expert 7 (expert and beyond), from the middle third of the book
Key technique
ALS-XZ
Hard steps
21 of 45 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 (×3), XY-Chain (×3), 2-String Kite (×2), WXYZ-Wing (×2), X-Wing/Swordfish (×2), Cell Forcing Chains, Finned Fish, Sue de Coq, XY-Wing, 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 (21)
  1. Step 8 · X-Wing/Swordfish advanced
    Rules out 8 from R3C7.
  2. Step 9 · ALS-XZ expert
    Rules out 7 from R9C9.
  3. Step 10 · Nice Loops/AICs expert
    Rules out 2 from R3C8.
  4. Step 11 · Nice Loops/AICs expert
    Rules out 2 from R8C2.
  5. Step 12 · Nice Loops/AICs expert
    Rules out 2 from R5C3.
  6. Step 13 · Cell Forcing Chains expert
    Rules out 5 from R1C5.
  7. Step 19 · 2-String Kite advanced
    Rules out 1 from R5C9.
  8. Step 20 · 2-String Kite advanced
    Rules out 4 from R5C9.
  9. Step 21 · XYZ-Wing advanced
    Rules out 7 from R5C8.
  10. Step 22 · XY-Chain expert
    Rules out 1 from R3C9.
  11. Step 25 · WXYZ-Wing expert
    Rules out 7 from R7C3.
  12. Step 26 · ALS-XZ expert
    Rules out 6 from R5C1.
  13. Step 27 · ALS-XZ expert
    Rules out 2 from R5C1.
  14. Step 28 · ALS-XZ expert
    Rules out 2 from R1C9.
  15. Step 29 · Finned Fish expert
    Rules out 2 from R4C3.
  16. Step 30 · WXYZ-Wing expert
    Rules out 6 from R1C8.
  17. Step 33 · X-Wing/Swordfish advanced
    Rules out 2 from R6C2.
  18. Step 34 · XY-Chain expert
    Rules out 3 from R4C2, R6C7.
  19. Step 37 · Sue de Coq expert
    Rules out 1 from R7C3; 4 from R8C3.
  20. Step 38 · XY-Chain expert
    Rules out 6 from R5C3.
  21. Step 40 · XY-Wing advanced
    Rules out 6 from R7C3.

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.