EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 64: 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 64 of 150 in Extreme Sudoku 1
Difficulty
Expert 5 (expert and beyond), from the middle third of the book
Key technique
Nice Loops/AICs
Hard steps
18 of 45 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: Nice Loops/AICs

An alternating chain of strong and weak links. Whichever end is true, the conclusion holds, so the digit at the marked cell is ruled out.

Other advanced and expert techniques in this solve: ALS-XZ (×2), Finned Fish (×2), Skyscraper (×2), XY-Chain (×2), 2-String Kite, Cell Forcing Chains, 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 (18)
  1. Step 5 · X-Wing/Swordfish advanced
    Rules out 3 from R2C5, R4C5, R5C5, R8C5 and 1 more.
  2. Step 6 · Skyscraper advanced
    Rules out 8 from R2C9, R9C8.
  3. Step 8 · XYZ-Wing advanced
    Rules out 7 from R6C8.
  4. Step 9 · Finned Fish expert
    Rules out 8 from R5C5.
  5. Step 10 · XY-Chain expert
    Rules out 7 from R6C1.
  6. Step 12 · ALS-XZ expert
    Rules out 5 from R2C1.
  7. Step 15 · 2-String Kite advanced
    Rules out 5 from R5C2.
  8. Step 17 · ALS-XZ expert
    Rules out 9 from R9C4.
  9. Step 18 · Nice Loops/AICs expert
    Rules out 6 from R1C2.
  10. Step 20 · Nice Loops/AICs expert
    Rules out 5 from R6C3.
  11. Step 21 · Nice Loops/AICs expert
    Rules out 3 from R9C3.
  12. Step 23 · Nice Loops/AICs expert
    Rules out 3 from R6C8.
  13. Step 25 · Nice Loops/AICs expert
    Rules out 2 from R6C4.
  14. Step 27 · Nice Loops/AICs expert
    Rules out 9 from R9C5.
  15. Step 28 · Cell Forcing Chains expert
    Rules out 9 from R1C3.
  16. Step 31 · Finned Fish expert
    Rules out 8 from R5C4.
  17. Step 34 · Skyscraper advanced
    Rules out 3 from R8C7, R9C6.
  18. Step 37 · XY-Chain expert
    Rules out 8 from R6C4.

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.