EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 60: 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 60 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
20 of 42 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 (×5), ALS-XZ (×3), XY-Wing (×2), Cell Forcing Chains, 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 (20)
  1. Step 6 · ALS-XZ expert
    Rules out 7 from R8C2.
  2. Step 7 · Nice Loops/AICs expert
    Rules out 7 from R8C1.
  3. Step 8 · Nice Loops/AICs expert
    Rules out 2 from R7C4; 1 from R9C4.
  4. Step 9 · Cell Forcing Chains expert
    Rules out 3 from R1C6.
  5. Step 12 · ALS-XZ expert
    Rules out 4 from R7C5.
  6. Step 14 · ALS-XZ expert
    Rules out 4 from R6C2.
  7. Step 15 · WXYZ-Wing expert
    Rules out 3 from R6C3.
  8. Step 16 · Nice Loops/AICs expert
    Rules out 3 from R7C5.
  9. Step 17 · Nice Loops/AICs expert
    Rules out 7 from R7C2.
  10. Step 18 · Nice Loops/AICs expert
    Rules out 7 from R4C2, R6C2.
  11. Step 21 · XYZ-Wing advanced
    Rules out 3 from R6C1.
  12. Step 24 · XY-Wing advanced
    Rules out 3 from R7C4.
  13. Step 25 · XY-Chain expert
    Rules out 1 from R9C7.
  14. Step 26 · XY-Chain expert
    Rules out 4 from R8C2.
  15. Step 27 · XY-Chain expert
    Rules out 1 from R9C6.
  16. Step 29 · XY-Chain expert
    Rules out 7 from R8C6.
  17. Step 30 · XY-Chain expert
    Rules out 1 from R8C6.
  18. Step 32 · XY-Chain expert
    Rules out 1 from R7C7.
  19. Step 34 · XY-Chain expert
    Rules out 1 from R1C8, R8C7.
  20. Step 38 · XY-Wing advanced
    Rules out 3 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.