EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 33: 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 33 of 150 in Extreme Sudoku 3
Difficulty
Expert 6 (expert and beyond), from the opening third of the book
Key technique
XY-Chain
Hard steps
25 of 49 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: XY-Chain

A chain of two-candidate cells, each linked to the next. Whichever way the start cell goes, one end of the chain holds the digit, so cells seeing both ends cannot.

Other advanced and expert techniques in this solve: ALS-XZ (×3), Empty Rectangle (×3), 2-String Kite (×2), Finned Fish (×2), Nice Loops/AICs (×2), X-Wing/Swordfish (×2), XY-Wing (×2), XYZ-Wing (×2), Cell Forcing Chains, 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 7 · X-Wing/Swordfish advanced
    Rules out 4 from R5C1, R5C5.
  2. Step 8 · Finned Fish expert
    Rules out 5 from R7C5.
  3. Step 9 · Finned Fish expert
    Rules out 5 from R8C6.
  4. Step 10 · ALS-XZ expert
    Rules out 1 from R9C4.
  5. Step 11 · ALS-XZ expert
    Rules out 2 from R9C4.
  6. Step 12 · ALS-XZ expert
    Rules out 5 from R9C9.
  7. Step 16 · W-Wing advanced
    Rules out 1 from R3C8.
  8. Step 17 · Empty Rectangle advanced
    Rules out 1 from R1C4.
  9. Step 18 · Empty Rectangle advanced
    Rules out 1 from R8C8.
  10. Step 19 · Nice Loops/AICs expert
    Rules out 1 from R5C1.
  11. Step 20 · Cell Forcing Chains expert
    Rules out 8 from R1C4.
  12. Step 22 · Empty Rectangle advanced
    Rules out 8 from R8C8.
  13. Step 24 · XYZ-Wing advanced
    Rules out 1 from R5C5.
  14. Step 25 · Sue de Coq expert
    Rules out 1 from R7C1, R9C2; 2 from R7C1.
  15. Step 26 · Nice Loops/AICs expert
    Rules out 8 from R3C9.
  16. Step 29 · XY-Wing advanced
    Rules out 1 from R7C3.
  17. Step 34 · 2-String Kite advanced
    Rules out 1 from R3C5.
  18. Step 35 · 2-String Kite advanced
    Rules out 1 from R1C6.
  19. Step 36 · X-Wing/Swordfish advanced
    Rules out 1 from R2C5.
  20. Step 37 · XY-Chain expert
    Rules out 3 from R5C6.
  21. Step 38 · XY-Chain expert
    Rules out 8 from R1C5.
  22. Step 39 · XY-Chain expert
    Rules out 8 from R2C5, R3C5, R5C6.
  23. Step 43 · XYZ-Wing advanced
    Rules out 3 from R5C2.
  24. Step 44 · XY-Chain expert
    Rules out 1 from R2C3.

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.