EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 59: 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 59 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 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: XY-Chain (×4), ALS-XZ (×3), Empty Rectangle (×3), WXYZ-Wing (×3), W-Wing (×2), Cell Forcing Chains, Finned Fish, Skyscraper, 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 (23)
  1. Step 5 · ALS-XZ expert
    Rules out 8 from R2C2, R7C3.
  2. Step 7 · Finned Fish expert
    Rules out 5 from R3C6.
  3. Step 8 · ALS-XZ expert
    Rules out 7 from R8C7.
  4. Step 10 · Nice Loops/AICs expert
    Rules out 5 from R1C5.
  5. Step 11 · X-Wing/Swordfish advanced
    Rules out 5 from R2C1, R3C1, R8C1.
  6. Step 12 · Nice Loops/AICs expert
    Rules out 9 from R9C9.
  7. Step 13 · Empty Rectangle advanced
    Rules out 9 from R2C8.
  8. Step 14 · Nice Loops/AICs expert
    Rules out 2 from R3C8.
  9. Step 15 · Cell Forcing Chains expert
    Rules out 9 from R1C1.
  10. Step 21 · W-Wing advanced
    Rules out 9 from R3C9.
  11. Step 22 · WXYZ-Wing expert
    Rules out 9 from R3C8.
  12. Step 23 · WXYZ-Wing expert
    Rules out 6 from R8C1.
  13. Step 24 · WXYZ-Wing expert
    Rules out 9 from R2C9.
  14. Step 26 · ALS-XZ expert
    Rules out 3 from R5C3.
  15. Step 27 · Nice Loops/AICs expert
    Rules out 9 from R3C6.
  16. Step 29 · Skyscraper advanced
    Rules out 9 from R8C7.
  17. Step 31 · Empty Rectangle advanced
    Rules out 9 from R4C7.
  18. Step 32 · Empty Rectangle advanced
    Rules out 9 from R5C2.
  19. Step 34 · W-Wing advanced
    Rules out 5 from R5C5, R6C3.
  20. Step 35 · XY-Chain expert
    Rules out 9 from R9C1.
  21. Step 37 · XY-Chain expert
    Rules out 2 from R3C7.
  22. Step 39 · XY-Chain expert
    Rules out 9 from R6C9.
  23. Step 41 · XY-Chain expert
    Rules out 6 from R5C5.

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.

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