EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 79: 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 79 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 52 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 (×5), Finned Fish (×2), WXYZ-Wing (×2), Cell Forcing Chains, Empty Rectangle, Skyscraper, 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 (24 of 25)
  1. Step 4 · Empty Rectangle advanced
    Rules out 4 from R9C8.
  2. Step 5 · Finned Fish expert
    Rules out 8 from R5C1, R6C1.
  3. Step 9 · Finned Fish expert
    Rules out 9 from R1C2.
  4. Step 10 · WXYZ-Wing expert
    Rules out 4 from R7C5.
  5. Step 11 · ALS-XZ expert
    Rules out 5 from R1C5.
  6. Step 12 · ALS-XZ expert
    Rules out 8 from R5C5.
  7. Step 13 · ALS-XZ expert
    Rules out 8 from R7C6.
  8. Step 15 · ALS-XZ expert
    Rules out 9 from R1C9.
  9. Step 16 · Nice Loops/AICs expert
    Rules out 8 from R1C2; 6 from R3C1.
  10. Step 20 · ALS-XZ expert
    Rules out 3 from R1C4.
  11. Step 21 · ALS-XZ expert
    Rules out 1 from R4C7.
  12. Step 22 · Nice Loops/AICs expert
    Rules out 9 from R3C1.
  13. Step 23 · Nice Loops/AICs expert
    Rules out 7 from R7C8.
  14. Step 24 · Nice Loops/AICs expert
    Rules out 7 from R7C6.
  15. Step 25 · Nice Loops/AICs expert
    Rules out 7 from R7C7.
  16. Step 26 · Cell Forcing Chains expert
    Rules out 3 from R1C5.
  17. Step 29 · Skyscraper advanced
    Rules out 3 from R1C9, R3C9, R5C7.
  18. Step 33 · WXYZ-Wing expert
    Rules out 5 from R9C6.
  19. Step 34 · Sue de Coq expert
    Rules out 2 from R5C5; 4 from R6C4.
  20. Step 38 · XY-Chain expert
    Rules out 8 from R5C4.
  21. Step 40 · XY-Chain expert
    Rules out 5 from R3C5.
  22. Step 41 · XY-Chain expert
    Rules out 4 from R4C6.
  23. Step 42 · XY-Chain expert
    Rules out 3 from R5C4.
  24. Step 43 · XY-Chain expert
    Rules out 6 from R7C6, R9C7, R9C9.

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.