EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 35: 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 35 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
16 of 35 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: ALS-XZ (×2), Finned Fish (×2), WXYZ-Wing (×2), 2-String Kite, Cell Forcing Chains, Empty Rectangle, Nice Loops/AICs, 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 (16)
  1. Step 4 · Empty Rectangle advanced
    Rules out 1 from R3C8.
  2. Step 5 · Finned Fish expert
    Rules out 1 from R2C8.
  3. Step 6 · XY-Chain expert
    Rules out 5 from R1C7, R3C4.
  4. Step 10 · ALS-XZ expert
    Rules out 9 from R2C2, R4C3.
  5. Step 12 · Finned Fish expert
    Rules out 3 from R8C3, R9C3.
  6. Step 13 · ALS-XZ expert
    Rules out 4 from R2C6, R3C3.
  7. Step 17 · 2-String Kite advanced
    Rules out 3 from R9C8.
  8. Step 18 · XY-Chain expert
    Rules out 1 from R5C2, R7C2, R9C2.
  9. Step 20 · XY-Chain expert
    Rules out 2 from R9C6.
  10. Step 21 · XY-Chain expert
    Rules out 3 from R2C5.
  11. Step 22 · XY-Chain expert
    Rules out 6 from R6C8.
  12. Step 23 · WXYZ-Wing expert
    Rules out 3 from R9C5.
  13. Step 24 · WXYZ-Wing expert
    Rules out 3 from R8C4, R9C4.
  14. Step 27 · X-Wing/Swordfish advanced
    Rules out 3 from R8C9.
  15. Step 28 · Nice Loops/AICs expert
    Rules out 1 from R8C8.
  16. Step 29 · Cell Forcing Chains expert
    Rules out 1 from R1C2.

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.