EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 148: 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 148 of 150 in Extreme Sudoku 1
Difficulty
Expert 6 (expert and beyond), from the final, hardest third of the book
Key technique
Finned Fish
Hard steps
22 of 48 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: 2-String Kite (×4), Nice Loops/AICs (×4), XY-Chain (×3), WXYZ-Wing (×2), XYZ-Wing (×2), ALS-XZ, Cell Forcing Chains, Empty Rectangle.

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 6 · 2-String Kite advanced
    Rules out 7 from R8C9.
  2. Step 7 · 2-String Kite advanced
    Rules out 9 from R6C7.
  3. Step 9 · Empty Rectangle advanced
    Rules out 7 from R8C5.
  4. Step 10 · Finned Fish expert
    Rules out 6 from R7C7.
  5. Step 11 · Finned Fish expert
    Rules out 7 from R7C5.
  6. Step 12 · Nice Loops/AICs expert
    Rules out 8 from R6C6.
  7. Step 14 · Nice Loops/AICs expert
    Rules out 8 from R7C6.
  8. Step 15 · Cell Forcing Chains expert
    Rules out 7 from R2C2.
  9. Step 19 · Finned Fish expert
    Rules out 6 from R9C9.
  10. Step 20 · XYZ-Wing advanced
    Rules out 4 from R3C9.
  11. Step 22 · WXYZ-Wing expert
    Rules out 1 from R4C1.
  12. Step 23 · ALS-XZ expert
    Rules out 9 from R7C7.
  13. Step 24 · Nice Loops/AICs expert
    Rules out 4 from R4C8.
  14. Step 25 · Nice Loops/AICs expert
    Rules out 6 from R4C9, R5C9.
  15. Step 26 · 2-String Kite advanced
    Rules out 6 from R8C6.
  16. Step 30 · 2-String Kite advanced
    Rules out 4 from R5C9.
  17. Step 31 · XYZ-Wing advanced
    Rules out 4 from R4C7.
  18. Step 32 · Finned Fish expert
    Rules out 6 from R9C6.
  19. Step 35 · XY-Chain expert
    Rules out 4 from R1C9, R8C8.
  20. Step 38 · XY-Chain expert
    Rules out 6 from R4C3, R7C1.
  21. Step 40 · XY-Chain expert
    Rules out 4 from R5C7.
  22. Step 41 · WXYZ-Wing expert
    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.