EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 1: 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 1 of 150 in Extreme Sudoku 2
Difficulty
Expert 5 (expert and beyond), from the opening third of the book
Key technique
Finned Fish
Hard steps
14 of 42 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), Nice Loops/AICs (×3), XY-Chain (×2), 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 (14)
  1. Step 7 · Finned Fish expert
    Rules out 1 from R7C5, R8C5.
  2. Step 8 · Finned Fish expert
    Rules out 2 from R6C9.
  3. Step 9 · XY-Chain expert
    Rules out 2 from R4C2, R4C3.
  4. Step 11 · ALS-XZ expert
    Rules out 1 from R1C9, R3C4, R3C6.
  5. Step 16 · ALS-XZ expert
    Rules out 2 from R6C1.
  6. Step 17 · ALS-XZ expert
    Rules out 7 from R6C4.
  7. Step 18 · Nice Loops/AICs expert
    Rules out 3 from R8C4.
  8. Step 23 · WXYZ-Wing expert
    Rules out 4 from R6C2.
  9. Step 24 · Nice Loops/AICs expert
    Rules out 8 from R8C4.
  10. Step 27 · Nice Loops/AICs expert
    Rules out 8 from R9C6.
  11. Step 30 · W-Wing advanced
    Rules out 5 from R8C8.
  12. Step 31 · Finned Fish expert
    Rules out 8 from R6C8, R6C9.
  13. Step 34 · XY-Wing advanced
    Rules out 4 from R4C5, R6C3.
  14. Step 37 · XY-Chain expert
    Rules out 9 from R1C3, R6C2.

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.