EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, 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 3
Difficulty
Expert 7 (expert and beyond), from the final, hardest third of the book
Key technique
Finned Fish
Hard steps
22 of 45 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 (×4), Nice Loops/AICs (×4), Empty Rectangle (×2), XY-Wing (×2), Cell Forcing Chains, Sue de Coq, WXYZ-Wing, X-Wing/Swordfish, XY-Chain, XYZ-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 (22)
  1. Step 6 · Sue de Coq expert
    Rules out 1 from R2C2, R3C2, R5C2; 2 from R5C2; 7 from R7C1.
  2. Step 9 · Empty Rectangle advanced
    Rules out 7 from R8C6.
  3. Step 10 · Finned Fish expert
    Rules out 1 from R4C6.
  4. Step 11 · ALS-XZ expert
    Rules out 9 from R5C8, R5C9.
  5. Step 12 · Cell Forcing Chains expert
    Rules out 1 from R1C3.
  6. Step 15 · Finned Fish expert
    Rules out 1 from R6C9.
  7. Step 16 · Nice Loops/AICs expert
    Rules out 1 from R6C6.
  8. Step 17 · Nice Loops/AICs expert
    Rules out 1 from R6C5.
  9. Step 18 · X-Wing/Swordfish advanced
    Rules out 1 from R1C1, R1C6, R1C9, R7C8.
  10. Step 20 · Empty Rectangle advanced
    Rules out 7 from R8C8.
  11. Step 21 · Finned Fish expert
    Rules out 7 from R7C4.
  12. Step 22 · ALS-XZ expert
    Rules out 9 from R6C8.
  13. Step 23 · ALS-XZ expert
    Rules out 2 from R1C5, R1C6.
  14. Step 24 · ALS-XZ expert
    Rules out 4 from R1C5.
  15. Step 25 · Nice Loops/AICs expert
    Rules out 1 from R5C9.
  16. Step 26 · Nice Loops/AICs expert
    Rules out 9 from R4C6.
  17. Step 29 · Finned Fish expert
    Rules out 2 from R7C4.
  18. Step 31 · XY-Chain expert
    Rules out 3 from R6C8, R9C9.
  19. Step 33 · WXYZ-Wing expert
    Rules out 7 from R8C7.
  20. Step 36 · XY-Wing advanced
    Rules out 7 from R1C1.
  21. Step 39 · XYZ-Wing advanced
    Rules out 2 from R8C6.
  22. Step 41 · XY-Wing advanced
    Rules out 2 from R7C3.

The book

Volume three: 150 new classic 9×9 grids, none repeated from books 1 or 2, 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.

On Amazon from 8 Dec About the book

Try a free sample puzzle (PDF) · prints on A4 or US Letter

More step-by-step solutions: Extreme Sudoku 1 · Extreme Killer Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Killer Sudoku 3.