EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 141: 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 141 of 150 in Extreme Sudoku 1
Difficulty
Expert 7 (expert and beyond), from the final, hardest third of the book
Key technique
Finned Fish
Hard steps
14 of 40 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 (×2), Nice Loops/AICs (×2), XY-Chain (×2), XY-Wing (×2), Cell Forcing Chains, Sue de Coq, WXYZ-Wing, 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 (14)
  1. Step 8 · Finned Fish expert
    Rules out 1 from R6C8.
  2. Step 9 · Finned Fish expert
    Rules out 4 from R4C5.
  3. Step 10 · WXYZ-Wing expert
    Rules out 6 from R3C3.
  4. Step 12 · XY-Chain expert
    Rules out 5 from R3C2, R8C1.
  5. Step 14 · Nice Loops/AICs expert
    Rules out 5 from R9C4.
  6. Step 15 · Nice Loops/AICs expert
    Rules out 9 from R9C4.
  7. Step 16 · Cell Forcing Chains expert
    Rules out 5 from R2C6, R7C6; 4 from R3C1, R5C2, R5C4, R5C6; 3 from R5C5, R6C2.
  8. Step 19 · X-Wing/Swordfish advanced
    Rules out 4 from R4C9, R9C5.
  9. Step 21 · XY-Chain expert
    Rules out 9 from R8C4.
  10. Step 22 · ALS-XZ expert
    Rules out 5 from R8C2, R9C5.
  11. Step 24 · Sue de Coq expert
    Rules out 7 from R7C8.
  12. Step 25 · ALS-XZ expert
    Rules out 5 from R7C5, R8C8.
  13. Step 29 · XY-Wing advanced
    Rules out 4 from R4C4, R7C5.
  14. Step 34 · XY-Wing advanced
    Rules out 9 from R1C6.

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.