EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 8: 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 8 of 150 in Extreme Sudoku 1
Difficulty
Expert 5 (expert and beyond), from the opening third of the book
Key technique
XY-Chain
Hard steps
23 of 44 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 (×4), 2-String Kite (×2), ALS-XZ (×2), Finned Fish (×2), W-Wing (×2), X-Wing/Swordfish (×2), XY-Wing (×2), Empty Rectangle, 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 (23)
  1. Step 5 · 2-String Kite advanced
    Rules out 3 from R9C5.
  2. Step 6 · 2-String Kite advanced
    Rules out 7 from R7C3.
  3. Step 7 · Finned Fish expert
    Rules out 6 from R1C8.
  4. Step 8 · ALS-XZ expert
    Rules out 2 from R6C7.
  5. Step 9 · Nice Loops/AICs expert
    Rules out 7 from R7C2.
  6. Step 10 · ALS-XZ expert
    Rules out 7 from R9C5, R9C6.
  7. Step 12 · XY-Chain expert
    Rules out 7 from R2C8.
  8. Step 13 · Nice Loops/AICs expert
    Rules out 7 from R3C2.
  9. Step 14 · Nice Loops/AICs expert
    Rules out 7 from R2C5.
  10. Step 16 · Nice Loops/AICs expert
    Rules out 1 from R1C8.
  11. Step 19 · WXYZ-Wing expert
    Rules out 2 from R1C9, R3C9.
  12. Step 22 · Empty Rectangle advanced
    Rules out 2 from R9C3.
  13. Step 23 · Finned Fish expert
    Rules out 2 from R3C1.
  14. Step 24 · XY-Wing advanced
    Rules out 6 from R3C9.
  15. Step 25 · W-Wing advanced
    Rules out 5 from R7C7.
  16. Step 30 · XY-Wing advanced
    Rules out 7 from R1C5.
  17. Step 31 · XY-Chain expert
    Rules out 6 from R1C5.
  18. Step 32 · XY-Chain expert
    Rules out 6 from R1C9.
  19. Step 35 · X-Wing/Swordfish advanced
    Rules out 2 from R6C8.
  20. Step 36 · W-Wing advanced
    Rules out 6 from R8C6.
  21. Step 38 · X-Wing/Swordfish advanced
    Rules out 7 from R8C5.
  22. Step 39 · XY-Chain expert
    Rules out 5 from R1C2, R7C3.
  23. Step 41 · XY-Chain expert
    Rules out 1 from R1C6, R6C5.

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.