EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 112: 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 112 of 150 in Extreme Sudoku 2
Difficulty
Expert 7 (expert and beyond), from the final, hardest third of the book
Key technique
WXYZ-Wing
Hard steps
18 of 34 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: WXYZ-Wing

Four cells holding four digits between them, where only one digit is not confined. That digit is removed from cells that see all its copies.

Other advanced and expert techniques in this solve: XY-Chain (×3), ALS-XZ (×2), Finned Fish (×2), Nice Loops/AICs (×2), Cell Forcing Chains, Sue de Coq, W-Wing, X-Wing/Swordfish, 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 (18)
  1. Step 4 · WXYZ-Wing expert
    Rules out 9 from R8C3, R9C3.
  2. Step 5 · W-Wing advanced
    Rules out 5 from R8C6.
  3. Step 6 · Finned Fish expert
    Rules out 9 from R4C7.
  4. Step 7 · WXYZ-Wing expert
    Rules out 3 from R1C2.
  5. Step 8 · Sue de Coq expert
    Rules out 8 from R7C1; 9 from R7C1.
  6. Step 9 · Nice Loops/AICs expert
    Rules out 9 from R8C2.
  7. Step 10 · Nice Loops/AICs expert
    Rules out 2 from R7C4.
  8. Step 11 · Cell Forcing Chains expert
    Rules out 8 from R1C2.
  9. Step 16 · Finned Fish expert
    Rules out 9 from R9C9.
  10. Step 17 · WXYZ-Wing expert
    Rules out 2 from R2C4.
  11. Step 18 · ALS-XZ expert
    Rules out 4 from R7C7.
  12. Step 19 · ALS-XZ expert
    Rules out 2 from R6C6.
  13. Step 21 · WXYZ-Wing expert
    Rules out 4 from R9C6.
  14. Step 22 · XY-Chain expert
    Rules out 6 from R3C9.
  15. Step 25 · X-Wing/Swordfish advanced
    Rules out 9 from R6C8, R6C9.
  16. Step 26 · XY-Chain expert
    Rules out 4 from R1C4.
  17. Step 28 · XYZ-Wing advanced
    Rules out 2 from R1C8.
  18. Step 30 · XY-Chain expert
    Rules out 3 from R1C4.

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.