EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 80: 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 80 of 150 in Extreme Sudoku 3
Difficulty
Expert 7 (expert and beyond), from the middle third of the book
Key technique
ALS-XZ
Hard steps
25 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: Nice Loops/AICs (×5), XY-Chain (×4), WXYZ-Wing (×3), 2-String Kite (×2), Cell Forcing Chains, Finned Fish, Sue de Coq, XY-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 (24 of 25)
  1. Step 4 · WXYZ-Wing expert
    Rules out 3 from R4C2, R7C1, R8C1.
  2. Step 5 · Sue de Coq expert
    Rules out 8 from R4C2; 4 from R6C9.
  3. Step 6 · 2-String Kite advanced
    Rules out 8 from R1C8.
  4. Step 7 · ALS-XZ expert
    Rules out 9 from R1C6, R2C6.
  5. Step 8 · ALS-XZ expert
    Rules out 4 from R4C4, R5C4, R6C4.
  6. Step 9 · ALS-XZ expert
    Rules out 6 from R1C9, R2C9.
  7. Step 11 · ALS-XZ expert
    Rules out 8 from R3C8, R6C7.
  8. Step 13 · Nice Loops/AICs expert
    Rules out 9 from R5C3.
  9. Step 18 · Finned Fish expert
    Rules out 6 from R1C8.
  10. Step 19 · XY-Chain expert
    Rules out 3 from R1C2.
  11. Step 21 · WXYZ-Wing expert
    Rules out 4 from R7C6.
  12. Step 22 · ALS-XZ expert
    Rules out 4 from R6C3.
  13. Step 24 · XY-Chain expert
    Rules out 3 from R9C2.
  14. Step 26 · XY-Chain expert
    Rules out 4 from R7C8.
  15. Step 27 · ALS-XZ expert
    Rules out 8 from R5C3.
  16. Step 28 · Nice Loops/AICs expert
    Rules out 4 from R5C3, R9C2.
  17. Step 30 · Nice Loops/AICs expert
    Rules out 6 from R1C3.
  18. Step 31 · Nice Loops/AICs expert
    Rules out 8 from R6C1.
  19. Step 33 · Nice Loops/AICs expert
    Rules out 8 from R2C3.
  20. Step 34 · Cell Forcing Chains expert
    Rules out 8 from R1C2.
  21. Step 39 · ALS-XZ expert
    Rules out 8 from R3C3.
  22. Step 40 · WXYZ-Wing expert
    Rules out 6 from R1C1.
  23. Step 43 · XY-Chain expert
    Rules out 3 from R2C4.
  24. Step 44 · 2-String Kite advanced
    Rules out 3 from R1C8.

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.