EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 39: 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 39 of 150 in Extreme Sudoku 2
Difficulty
Expert 6 (expert and beyond), from the opening third of the book
Key technique
XY-Chain
Hard steps
19 of 41 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: XY-Chain

A chain of two-candidate cells, each linked to the next. Whichever way the start cell goes, one end of the chain holds the digit, so cells seeing both ends cannot.

Other advanced and expert techniques in this solve: Nice Loops/AICs (×3), 2-String Kite (×2), XY-Wing (×2), ALS-XZ, Cell Forcing Chains, Finned Fish, W-Wing, 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 (19)
  1. Step 6 · Finned Fish expert
    Rules out 1 from R8C9.
  2. Step 7 · WXYZ-Wing expert
    Rules out 4 from R4C1, R4C3.
  3. Step 9 · 2-String Kite advanced
    Rules out 5 from R9C7.
  4. Step 10 · 2-String Kite advanced
    Rules out 6 from R9C4.
  5. Step 11 · Nice Loops/AICs expert
    Rules out 5 from R7C3.
  6. Step 12 · Cell Forcing Chains expert
    Rules out 1 from R4C8.
  7. Step 15 · XY-Wing advanced
    Rules out 4 from R3C4.
  8. Step 16 · W-Wing advanced
    Rules out 6 from R8C5.
  9. Step 17 · X-Wing/Swordfish advanced
    Rules out 6 from R4C3, R9C3.
  10. Step 18 · ALS-XZ expert
    Rules out 6 from R2C2.
  11. Step 20 · Nice Loops/AICs expert
    Rules out 5 from R8C2.
  12. Step 21 · Nice Loops/AICs expert
    Rules out 5 from R7C2.
  13. Step 26 · XY-Chain expert
    Rules out 1 from R4C9.
  14. Step 27 · XY-Chain expert
    Rules out 9 from R8C7.
  15. Step 28 · XY-Chain expert
    Rules out 6 from R8C2.
  16. Step 29 · XY-Chain expert
    Rules out 7 from R7C7, R9C3.
  17. Step 32 · XY-Wing advanced
    Rules out 6 from R7C9.
  18. Step 34 · XY-Chain expert
    Rules out 6 from R2C8.
  19. Step 38 · XY-Chain expert
    Rules out 6 from R4C5.

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.