EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 73: 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 73 of 150 in Extreme Sudoku 1
Difficulty
Expert 5 (expert and beyond), from the middle third of the book
Key technique
XY-Chain
Hard steps
32 of 55 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 (×5), Nice Loops/AICs (×4), Finned Fish (×3), W-Wing (×3), Skyscraper (×2), WXYZ-Wing, X-Wing/Swordfish, 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 (24 of 32)
  1. Step 3 · Skyscraper advanced
    Rules out 2 from R4C7, R4C9, R6C3.
  2. Step 7 · XYZ-Wing advanced
    Rules out 9 from R4C1, R4C3.
  3. Step 8 · ALS-XZ expert
    Rules out 1 from R1C4.
  4. Step 9 · ALS-XZ expert
    Rules out 9 from R8C3.
  5. Step 10 · Skyscraper advanced
    Rules out 9 from R4C2.
  6. Step 12 · ALS-XZ expert
    Rules out 7 from R9C4, R9C5, R9C6.
  7. Step 13 · Nice Loops/AICs expert
    Rules out 2 from R3C4.
  8. Step 15 · Finned Fish expert
    Rules out 7 from R8C5.
  9. Step 16 · ALS-XZ expert
    Rules out 3 from R8C5.
  10. Step 17 · Nice Loops/AICs expert
    Rules out 7 from R2C9.
  11. Step 18 · Nice Loops/AICs expert
    Rules out 7 from R7C9.
  12. Step 20 · Nice Loops/AICs expert
    Rules out 9 from R6C4.
  13. Step 23 · ALS-XZ expert
    Rules out 4 from R2C7.
  14. Step 24 · W-Wing advanced
    Rules out 7 from R2C6.
  15. Step 25 · XY-Chain expert
    Rules out 4 from R4C3.
  16. Step 26 · XY-Chain expert
    Rules out 1 from R1C2.
  17. Step 27 · XY-Chain expert
    Rules out 7 from R9C7.
  18. Step 28 · WXYZ-Wing expert
    Rules out 1 from R4C1.
  19. Step 34 · W-Wing advanced
    Rules out 1 from R8C2.
  20. Step 35 · XY-Chain expert
    Rules out 1 from R1C1, R1C5.
  21. Step 36 · Finned Fish expert
    Rules out 1 from R7C4, R7C5.
  22. Step 37 · Finned Fish expert
    Rules out 1 from R8C4.
  23. Step 39 · XY-Chain expert
    Rules out 7 from R8C9.
  24. Step 41 · XY-Chain expert
    Rules out 4 from R3C4.

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.