EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 144: 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 144 of 150 in Extreme Sudoku 2
Difficulty
Expert 6 (expert and beyond), from the final, hardest third of the book
Key technique
Finned Fish
Hard steps
14 of 39 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 (×3), Nice Loops/AICs (×2), XY-Chain (×2), ALS-XZ, Cell Forcing Chains, Empty Rectangle, W-Wing, WXYZ-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 · 2-String Kite advanced
    Rules out 2 from R8C5.
  2. Step 8 · Empty Rectangle advanced
    Rules out 6 from R1C8.
  3. Step 10 · Finned Fish expert
    Rules out 2 from R8C4.
  4. Step 11 · Cell Forcing Chains expert
    Rules out 9 from R3C8.
  5. Step 19 · WXYZ-Wing expert
    Rules out 7 from R5C5.
  6. Step 23 · 2-String Kite advanced
    Rules out 9 from R7C4.
  7. Step 24 · Finned Fish expert
    Rules out 9 from R9C4.
  8. Step 25 · ALS-XZ expert
    Rules out 8 from R8C4.
  9. Step 26 · Nice Loops/AICs expert
    Rules out 3 from R2C9.
  10. Step 27 · Nice Loops/AICs expert
    Rules out 9 from R8C4.
  11. Step 28 · W-Wing advanced
    Rules out 1 from R1C5, R3C5, R5C6.
  12. Step 32 · 2-String Kite advanced
    Rules out 8 from R9C6.
  13. Step 34 · XY-Chain expert
    Rules out 6 from R1C3, R9C1.
  14. Step 36 · XY-Chain expert
    Rules out 2 from R2C2, R7C3.

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.