EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 98: 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 98 of 150 in Extreme Sudoku 3
Difficulty
Expert 6 (expert and beyond), from the middle third of the book
Key technique
ALS-XZ
Hard steps
18 of 38 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), Finned Fish (×2), XY-Chain (×2), XY-Wing (×2), Cell Forcing Chains, Empty Rectangle, Skyscraper, Sue de Coq, W-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 (18)
  1. Step 5 · Skyscraper advanced
    Rules out 9 from R7C9, R9C5.
  2. Step 7 · Empty Rectangle advanced
    Rules out 6 from R3C8.
  3. Step 8 · Finned Fish expert
    Rules out 6 from R3C7.
  4. Step 9 · Finned Fish expert
    Rules out 9 from R1C5.
  5. Step 10 · ALS-XZ expert
    Rules out 6 from R5C5.
  6. Step 11 · ALS-XZ expert
    Rules out 5 from R5C9.
  7. Step 12 · Nice Loops/AICs expert
    Rules out 4 from R4C5.
  8. Step 13 · Nice Loops/AICs expert
    Rules out 6 from R6C5.
  9. Step 14 · Cell Forcing Chains expert
    Rules out 5 from R3C8.
  10. Step 16 · Sue de Coq expert
    Rules out 2 from R3C7, R5C9, R6C9; 5 from R6C9.
  11. Step 17 · Nice Loops/AICs expert
    Rules out 9 from R5C4.
  12. Step 23 · ALS-XZ expert
    Rules out 3 from R5C3, R6C6.
  13. Step 27 · XY-Wing advanced
    Rules out 6 from R6C7.
  14. Step 28 · W-Wing advanced
    Rules out 5 from R6C7.
  15. Step 31 · XY-Chain expert
    Rules out 2 from R1C9, R2C5.
  16. Step 32 · XY-Chain expert
    Rules out 2 from R1C2.
  17. Step 34 · X-Wing/Swordfish advanced
    Rules out 4 from R2C2, R2C6.
  18. Step 35 · XY-Wing advanced
    Rules out 4 from R2C1.

The book

Volume three: 150 new classic 9×9 grids, none repeated from books 1 or 2, 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.

On Amazon from 8 Dec About the book

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