EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 19: 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 19 of 150 in Extreme Sudoku 3
Difficulty
Expert 5 (expert and beyond), from the opening third of the book
Key technique
ALS-XZ
Hard steps
15 of 31 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), XY-Chain (×3), W-Wing (×2), 2-String Kite, Finned Fish, WXYZ-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 (15)
  1. Step 3 · 2-String Kite advanced
    Rules out 2 from R6C9.
  2. Step 4 · W-Wing advanced
    Rules out 8 from R1C6, R2C8, R2C9.
  3. Step 5 · Finned Fish expert
    Rules out 2 from R6C8.
  4. Step 6 · WXYZ-Wing expert
    Rules out 8 from R7C4, R9C4.
  5. Step 10 · ALS-XZ expert
    Rules out 5 from R2C9.
  6. Step 12 · ALS-XZ expert
    Rules out 8 from R7C1.
  7. Step 13 · ALS-XZ expert
    Rules out 3 from R2C1.
  8. Step 14 · Nice Loops/AICs expert
    Rules out 8 from R6C7.
  9. Step 15 · Nice Loops/AICs expert
    Rules out 8 from R2C5.
  10. Step 16 · Nice Loops/AICs expert
    Rules out 8 from R3C5.
  11. Step 23 · XY-Chain expert
    Rules out 8 from R2C1.
  12. Step 24 · ALS-XZ expert
    Rules out 3 from R9C3.
  13. Step 26 · W-Wing advanced
    Rules out 8 from R9C1.
  14. Step 27 · XY-Chain expert
    Rules out 3 from R7C6, R9C1, R9C2.
  15. Step 29 · XY-Chain expert
    Rules out 7 from R1C1.

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.