EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 8: 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 8 of 150 in Extreme Sudoku 3
Difficulty
Expert 5 (expert and beyond), from the opening third of the book
Key technique
Nice Loops/AICs
Hard steps
19 of 44 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 (×4), WXYZ-Wing (×2), XY-Chain (×2), 2-String Kite, Empty Rectangle, Skyscraper, 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 (19)
  1. Step 6 · Skyscraper advanced
    Rules out 7 from R3C6, R9C5.
  2. Step 7 · 2-String Kite advanced
    Rules out 8 from R8C6.
  3. Step 8 · WXYZ-Wing expert
    Rules out 5 from R1C1, R2C9.
  4. Step 10 · XY-Wing advanced
    Rules out 2 from R2C8, R3C8.
  5. Step 14 · ALS-XZ expert
    Rules out 3 from R3C2.
  6. Step 16 · Nice Loops/AICs expert
    Rules out 8 from R8C5.
  7. Step 17 · Nice Loops/AICs expert
    Rules out 8 from R9C5.
  8. Step 18 · WXYZ-Wing expert
    Rules out 4 from R5C5.
  9. Step 19 · Nice Loops/AICs expert
    Rules out 5 from R9C3.
  10. Step 21 · ALS-XZ expert
    Rules out 8 from R9C1.
  11. Step 22 · ALS-XZ expert
    Rules out 3 from R2C2.
  12. Step 23 · Nice Loops/AICs expert
    Rules out 5 from R8C4.
  13. Step 24 · Sue de Coq expert
    Rules out 2 from R8C5.
  14. Step 25 · Nice Loops/AICs expert
    Rules out 5 from R7C6.
  15. Step 26 · Nice Loops/AICs expert
    Rules out 7 from R7C1.
  16. Step 30 · Empty Rectangle advanced
    Rules out 8 from R5C5.
  17. Step 31 · ALS-XZ expert
    Rules out 7 from R3C3.
  18. Step 35 · XY-Chain expert
    Rules out 8 from R4C1.
  19. Step 38 · XY-Chain expert
    Rules out 4 from R9C2.

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

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More step-by-step solutions: Extreme Sudoku 1 · Extreme Killer Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Killer Sudoku 3.