EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 113: 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 113 of 150 in Extreme Sudoku 2
Difficulty
Expert 7 (expert and beyond), from the final, hardest third of the book
Key technique
Finned Fish
Hard steps
22 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: Finned Fish

An X-Wing or Swordfish with one extra candidate (the fin). Cells that are in the fish pattern and also see the fin lose the digit.

Other advanced and expert techniques in this solve: Nice Loops/AICs (×3), XY-Chain (×3), Skyscraper (×2), W-Wing (×2), 2-String Kite, ALS-XZ, Cell Forcing Chains, Empty Rectangle, Sue de Coq, WXYZ-Wing, X-Wing/Swordfish, XY-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 (22)
  1. Step 5 · Skyscraper advanced
    Rules out 4 from R7C6, R8C3.
  2. Step 8 · 2-String Kite advanced
    Rules out 5 from R9C6.
  3. Step 9 · Empty Rectangle advanced
    Rules out 2 from R7C4.
  4. Step 10 · Finned Fish expert
    Rules out 3 from R5C2.
  5. Step 11 · Finned Fish expert
    Rules out 6 from R4C8, R6C8.
  6. Step 13 · WXYZ-Wing expert
    Rules out 9 from R6C2.
  7. Step 14 · Sue de Coq expert
    Rules out 1 from R7C4; 3 from R7C6; 2 from R9C2.
  8. Step 15 · Finned Fish expert
    Rules out 2 from R8C4.
  9. Step 16 · ALS-XZ expert
    Rules out 2 from R7C6.
  10. Step 17 · Nice Loops/AICs expert
    Rules out 9 from R4C5.
  11. Step 18 · Nice Loops/AICs expert
    Rules out 5 from R5C8.
  12. Step 19 · Nice Loops/AICs expert
    Rules out 1 from R6C2.
  13. Step 20 · Cell Forcing Chains expert
    Rules out 3 from R1C7.
  14. Step 23 · W-Wing advanced
    Rules out 9 from R4C4.
  15. Step 26 · XY-Chain expert
    Rules out 3 from R7C2.
  16. Step 27 · XY-Chain expert
    Rules out 9 from R7C2.
  17. Step 28 · Skyscraper advanced
    Rules out 9 from R5C4, R8C5.
  18. Step 30 · XYZ-Wing advanced
    Rules out 5 from R5C6.
  19. Step 31 · X-Wing/Swordfish advanced
    Rules out 5 from R7C4.
  20. Step 37 · W-Wing advanced
    Rules out 1 from R7C1.
  21. Step 38 · XY-Chain expert
    Rules out 9 from R5C3, R8C2.
  22. Step 40 · XY-Wing advanced
    Rules out 9 from R4C2, R5C9.

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.