EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 13: 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 13 of 150 in Extreme Sudoku 3
Difficulty
Expert 6 (expert and beyond), from the opening third of the book
Key technique
Nice Loops/AICs
Hard steps
22 of 46 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: Nice Loops/AICs

An alternating chain of strong and weak links. Whichever end is true, the conclusion holds, so the digit at the marked cell is ruled out.

Other advanced and expert techniques in this solve: ALS-XZ (×6), XY-Chain (×3), 2-String Kite, Finned Fish, Skyscraper, Sue de Coq, WXYZ-Wing, X-Wing/Swordfish.

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 (22)
  1. Step 5 · 2-String Kite advanced
    Rules out 6 from R6C7.
  2. Step 6 · WXYZ-Wing expert
    Rules out 1 from R7C8, R8C8.
  3. Step 7 · ALS-XZ expert
    Rules out 3 from R6C1, R9C1.
  4. Step 8 · Nice Loops/AICs expert
    Rules out 4 from R1C2.
  5. Step 9 · Nice Loops/AICs expert
    Rules out 7 from R6C4.
  6. Step 10 · Nice Loops/AICs expert
    Rules out 7 from R1C3.
  7. Step 11 · Nice Loops/AICs expert
    Rules out 1 from R7C3.
  8. Step 12 · Nice Loops/AICs expert
    Rules out 1 from R2C1.
  9. Step 13 · Nice Loops/AICs expert
    Rules out 8 from R3C1.
  10. Step 14 · ALS-XZ expert
    Rules out 1 from R1C1.
  11. Step 15 · ALS-XZ expert
    Rules out 1 from R6C7.
  12. Step 16 · Nice Loops/AICs expert
    Rules out 7 from R1C1, R1C2.
  13. Step 18 · ALS-XZ expert
    Rules out 2 from R1C3.
  14. Step 20 · Finned Fish expert
    Rules out 1 from R2C2.
  15. Step 21 · ALS-XZ expert
    Rules out 8 from R1C1.
  16. Step 25 · X-Wing/Swordfish advanced
    Rules out 1 from R4C9, R8C9.
  17. Step 26 · XY-Chain expert
    Rules out 8 from R3C9, R8C8, R9C8.
  18. Step 30 · XY-Chain expert
    Rules out 7 from R3C2, R3C8.
  19. Step 32 · XY-Chain expert
    Rules out 7 from R4C3.
  20. Step 33 · Sue de Coq expert
    Rules out 1 from R5C7.
  21. Step 34 · ALS-XZ expert
    Rules out 5 from R2C4.
  22. Step 41 · Skyscraper advanced
    Rules out 6 from R5C7, R8C9.

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.