EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 40: 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 40 of 150 in Extreme Sudoku 1
Difficulty
Expert 7 (expert and beyond), from the opening third of the book
Key technique
Finned Fish
Hard steps
11 of 31 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 (×2), 2-String Kite, ALS-XZ, Cell Forcing Chains, Sue de Coq, WXYZ-Wing, XY-Chain, 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 (11)
  1. Step 6 · 2-String Kite advanced
    Rules out 1 from R9C6.
  2. Step 7 · Finned Fish expert
    Rules out 3 from R6C4.
  3. Step 8 · WXYZ-Wing expert
    Rules out 6 from R1C1.
  4. Step 9 · Sue de Coq expert
    Rules out 6 from R9C3.
  5. Step 10 · Nice Loops/AICs expert
    Rules out 7 from R1C4.
  6. Step 12 · Nice Loops/AICs expert
    Rules out 1 from R1C9.
  7. Step 13 · Cell Forcing Chains expert
    Rules out 2 from R1C1.
  8. Step 16 · ALS-XZ expert
    Rules out 7 from R4C8.
  9. Step 18 · Finned Fish expert
    Rules out 6 from R8C2.
  10. Step 19 · XY-Chain expert
    Rules out 1 from R1C7, R8C9, R9C9.
  11. Step 23 · XY-Wing advanced
    Rules out 6 from R5C7.

The book

Classic 9×9 sudoku with the warm-up taken out. Every grid sits at the top of the expert range or beyond it, and the book ramps from hard to brutal.

150 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 Killer Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.