EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 68: 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 68 of 150 in Extreme Sudoku 2
Difficulty
Expert 6 (expert and beyond), from the middle third of the book
Key technique
Nice Loops/AICs
Hard steps
23 of 50 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), Finned Fish (×2), W-Wing (×2), WXYZ-Wing (×2), Cell Forcing Chains, Skyscraper, XY-Chain.

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 (23)
  1. Step 5 · WXYZ-Wing expert
    Rules out 1 from R4C7, R5C7, R9C9.
  2. Step 10 · W-Wing advanced
    Rules out 4 from R3C7, R5C4.
  3. Step 11 · Finned Fish expert
    Rules out 9 from R6C6.
  4. Step 12 · ALS-XZ expert
    Rules out 3 from R8C7.
  5. Step 13 · ALS-XZ expert
    Rules out 4 from R1C6, R3C6, R6C4.
  6. Step 14 · Nice Loops/AICs expert
    Rules out 2 from R6C3.
  7. Step 15 · Nice Loops/AICs expert
    Rules out 2 from R3C3.
  8. Step 16 · Nice Loops/AICs expert
    Rules out 8 from R2C2.
  9. Step 17 · Nice Loops/AICs expert
    Rules out 4 from R2C7.
  10. Step 18 · Nice Loops/AICs expert
    Rules out 4 from R1C7.
  11. Step 19 · Nice Loops/AICs expert
    Rules out 9 from R5C1.
  12. Step 21 · ALS-XZ expert
    Rules out 9 from R1C3.
  13. Step 24 · Nice Loops/AICs expert
    Rules out 9 from R2C5.
  14. Step 27 · ALS-XZ expert
    Rules out 6 from R2C8.
  15. Step 28 · Nice Loops/AICs expert
    Rules out 2 from R1C1.
  16. Step 29 · Nice Loops/AICs expert
    Rules out 3 from R2C7.
  17. Step 32 · Nice Loops/AICs expert
    Rules out 2 from R6C1.
  18. Step 33 · Cell Forcing Chains expert
    Rules out 1 from R2C2.
  19. Step 36 · WXYZ-Wing expert
    Rules out 6 from R3C6.
  20. Step 39 · Skyscraper advanced
    Rules out 6 from R4C5, R5C1.
  21. Step 44 · W-Wing advanced
    Rules out 5 from R8C7.
  22. Step 45 · Finned Fish expert
    Rules out 5 from R3C8.
  23. Step 46 · XY-Chain expert
    Rules out 8 from R1C3, R7C1.

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.