EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 74: 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 74 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
23 of 52 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), Cell Forcing Chains, Skyscraper, W-Wing, WXYZ-Wing, 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 (23)
  1. Step 7 · ALS-XZ expert
    Rules out 8 from R1C7.
  2. Step 8 · ALS-XZ expert
    Rules out 4 from R3C9.
  3. Step 9 · Nice Loops/AICs expert
    Rules out 9 from R5C7, R5C9.
  4. Step 12 · XYZ-Wing advanced
    Rules out 5 from R9C9.
  5. Step 13 · WXYZ-Wing expert
    Rules out 8 from R2C3.
  6. Step 14 · Nice Loops/AICs expert
    Rules out 2 from R1C3.
  7. Step 17 · Nice Loops/AICs expert
    Rules out 3 from R5C2.
  8. Step 18 · ALS-XZ expert
    Rules out 1 from R3C2.
  9. Step 19 · ALS-XZ expert
    Rules out 8 from R3C2.
  10. Step 20 · Nice Loops/AICs expert
    Rules out 3 from R9C7.
  11. Step 21 · Cell Forcing Chains expert
    Rules out 8 from R1C4.
  12. Step 24 · W-Wing advanced
    Rules out 6 from R1C7.
  13. Step 25 · XY-Chain expert
    Rules out 3 from R3C9, R8C7.
  14. Step 26 · ALS-XZ expert
    Rules out 8 from R3C7.
  15. Step 31 · XY-Chain expert
    Rules out 4 from R1C7.
  16. Step 34 · XY-Chain expert
    Rules out 6 from R2C9.
  17. Step 36 · XY-Chain expert
    Rules out 8 from R2C2.
  18. Step 38 · XY-Chain expert
    Rules out 4 from R1C6.
  19. Step 39 · XY-Chain expert
    Rules out 8 from R5C3, R8C2.
  20. Step 41 · XY-Chain expert
    Rules out 1 from R8C1.
  21. Step 43 · Skyscraper advanced
    Rules out 8 from R1C6, R3C1.
  22. Step 45 · XY-Chain expert
    Rules out 9 from R5C3, R6C6.
  23. Step 48 · XY-Chain expert
    Rules out 8 from R8C1.

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.