EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 24: 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 24 of 150 in Extreme Sudoku 2
Difficulty
Expert 6 (expert and beyond), from the opening third of the book
Key technique
Nice Loops/AICs
Hard steps
26 of 45 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 (×3), 2-String Kite (×2), Finned Fish (×2), Skyscraper (×2), WXYZ-Wing (×2), Cell Forcing Chains, Empty Rectangle, Sue de Coq, W-Wing, XYZ-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 26)
  1. Step 3 · ALS-XZ expert
    Rules out 6 from R3C3.
  2. Step 4 · Nice Loops/AICs expert
    Rules out 3 from R2C1.
  3. Step 5 · Nice Loops/AICs expert
    Rules out 6 from R5C1.
  4. Step 8 · 2-String Kite advanced
    Rules out 2 from R1C9.
  5. Step 9 · Finned Fish expert
    Rules out 7 from R5C4.
  6. Step 10 · Nice Loops/AICs expert
    Rules out 8 from R4C3.
  7. Step 11 · Nice Loops/AICs expert
    Rules out 6 from R6C2.
  8. Step 13 · 2-String Kite advanced
    Rules out 7 from R5C8.
  9. Step 14 · XYZ-Wing advanced
    Rules out 8 from R6C4, R6C6.
  10. Step 15 · Nice Loops/AICs expert
    Rules out 3 from R2C7.
  11. Step 18 · Nice Loops/AICs expert
    Rules out 7 from R8C3.
  12. Step 19 · Nice Loops/AICs expert
    Rules out 8 from R6C8.
  13. Step 20 · Nice Loops/AICs expert
    Rules out 7 from R9C5.
  14. Step 22 · Nice Loops/AICs expert
    Rules out 8 from R2C9.
  15. Step 23 · Nice Loops/AICs expert
    Rules out 8 from R1C9.
  16. Step 24 · Cell Forcing Chains expert
    Rules out 3 from R1C1.
  17. Step 27 · Skyscraper advanced
    Rules out 9 from R3C3, R9C2.
  18. Step 28 · Empty Rectangle advanced
    Rules out 8 from R3C9.
  19. Step 29 · WXYZ-Wing expert
    Rules out 5 from R1C8, R2C5.
  20. Step 32 · W-Wing advanced
    Rules out 8 from R5C4.
  21. Step 34 · Skyscraper advanced
    Rules out 8 from R3C4, R8C6.
  22. Step 35 · WXYZ-Wing expert
    Rules out 9 from R3C7.
  23. Step 36 · ALS-XZ expert
    Rules out 9 from R5C8.
  24. Step 37 · Sue de Coq expert
    Rules out 8 from R8C8.

The book

Volume two: 150 new classic 9×9 grids, none repeated from book 1, 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.

Buy on Amazon US Buy on Amazon UK
Other Amazon stores
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 Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.