EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 36: 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 36 of 150 in Extreme Sudoku 2
Difficulty
Expert 7 (expert and beyond), from the opening third of the book
Key technique
Finned Fish
Hard steps
21 of 43 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: ALS-XZ (×3), Skyscraper (×3), XY-Chain (×2), 2-String Kite, Coloring/Multi-coloring, Nice Loops/AICs, Sue de Coq, W-Wing, WXYZ-Wing, 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 (21)
  1. Step 5 · Finned Fish expert
    Rules out 1 from R7C5.
  2. Step 6 · Finned Fish expert
    Rules out 1 from R1C7.
  3. Step 7 · Finned Fish expert
    Rules out 1 from R2C7.
  4. Step 8 · Finned Fish expert
    Rules out 9 from R3C6.
  5. Step 9 · Sue de Coq expert
    Rules out 7 from R1C7; 2 from R2C2, R2C4, R2C5; 8 from R2C2, R2C4, R2C5, R2C6.
  6. Step 10 · 2-String Kite advanced
    Rules out 7 from R2C4.
  7. Step 11 · Finned Fish expert
    Rules out 7 from R2C5.
  8. Step 12 · ALS-XZ expert
    Rules out 2 from R1C3.
  9. Step 13 · ALS-XZ expert
    Rules out 7 from R1C5, R7C3.
  10. Step 15 · W-Wing advanced
    Rules out 2 from R7C1.
  11. Step 17 · Skyscraper advanced
    Rules out 2 from R2C9, R5C7.
  12. Step 19 · Coloring/Multi-coloring expert
    Rules out 1 from R6C2.
  13. Step 20 · WXYZ-Wing expert
    Rules out 9 from R6C1.
  14. Step 22 · XY-Wing advanced
    Rules out 8 from R1C7, R2C1.
  15. Step 24 · XY-Chain expert
    Rules out 8 from R8C3, R9C3.
  16. Step 25 · ALS-XZ expert
    Rules out 8 from R9C6.
  17. Step 26 · Finned Fish expert
    Rules out 8 from R1C5.
  18. Step 27 · XY-Chain expert
    Rules out 9 from R1C6, R4C5.
  19. Step 29 · Skyscraper advanced
    Rules out 1 from R8C7.
  20. Step 30 · Nice Loops/AICs expert
    Rules out 8 from R4C3.
  21. Step 37 · Skyscraper advanced
    Rules out 7 from R3C4, R5C6.

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.