EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 28: 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 28 of 150 in Extreme Sudoku 3
Difficulty
Expert 6 (expert and beyond), from the opening third of the book
Key technique
ALS-XZ
Hard steps
18 of 40 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 (×2), WXYZ-Wing (×2), X-Wing/Swordfish (×2), XY-Chain (×2), XY-Wing (×2), 2-String Kite, Finned Fish, Sue de Coq, W-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 6 · Nice Loops/AICs expert
    Rules out 1 from R2C8.
  2. Step 9 · ALS-XZ expert
    Rules out 2 from R5C5.
  3. Step 10 · ALS-XZ expert
    Rules out 5 from R7C5.
  4. Step 11 · ALS-XZ expert
    Rules out 5 from R4C3.
  5. Step 12 · 2-String Kite advanced
    Rules out 5 from R5C5.
  6. Step 13 · WXYZ-Wing expert
    Rules out 5 from R6C4, R6C6.
  7. Step 14 · X-Wing/Swordfish advanced
    Rules out 5 from R1C2, R1C5.
  8. Step 15 · W-Wing advanced
    Rules out 8 from R1C8, R2C5.
  9. Step 17 · WXYZ-Wing expert
    Rules out 3 from R6C7, R6C9.
  10. Step 18 · Sue de Coq expert
    Rules out 3 from R1C1, R1C3, R3C3; 2 from R2C7.
  11. Step 19 · XY-Wing advanced
    Rules out 8 from R1C3, R3C4, R3C5, R3C6.
  12. Step 24 · XY-Chain expert
    Rules out 6 from R1C7, R6C8.
  13. Step 26 · XY-Chain expert
    Rules out 2 from R3C4, R6C8.
  14. Step 27 · ALS-XZ expert
    Rules out 3 from R5C3.
  15. Step 28 · XY-Wing advanced
    Rules out 2 from R5C4.
  16. Step 29 · Finned Fish expert
    Rules out 3 from R2C7.
  17. Step 30 · Nice Loops/AICs expert
    Rules out 9 from R1C3, R7C1.
  18. Step 35 · X-Wing/Swordfish advanced
    Rules out 2 from R1C5.

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

Try a free sample puzzle (PDF) · prints on A4 or US Letter

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