EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, 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 2
Difficulty
Expert 6 (expert and beyond), from the middle third of the book
Key technique
Nice Loops/AICs
Hard steps
25 of 48 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 (×5), Finned Fish (×3), Skyscraper (×2), XY-Chain (×2), Cell Forcing Chains, Empty Rectangle, Sue de Coq, 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 25)
  1. Step 4 · Empty Rectangle advanced
    Rules out 1 from R5C7.
  2. Step 5 · Finned Fish expert
    Rules out 2 from R9C5.
  3. Step 6 · ALS-XZ expert
    Rules out 1 from R7C6.
  4. Step 7 · Nice Loops/AICs expert
    Rules out 8 from R5C4.
  5. Step 8 · Nice Loops/AICs expert
    Rules out 1 from R7C4.
  6. Step 9 · Nice Loops/AICs expert
    Rules out 2 from R9C7.
  7. Step 10 · Nice Loops/AICs expert
    Rules out 6 from R9C7.
  8. Step 11 · Cell Forcing Chains expert
    Rules out 2 from R2C8.
  9. Step 14 · Skyscraper advanced
    Rules out 2 from R2C7, R3C2.
  10. Step 17 · Nice Loops/AICs expert
    Rules out 8 from R5C7.
  11. Step 19 · ALS-XZ expert
    Rules out 3 from R7C7.
  12. Step 20 · XYZ-Wing advanced
    Rules out 1 from R3C7.
  13. Step 21 · ALS-XZ expert
    Rules out 1 from R9C8, R9C9.
  14. Step 23 · Finned Fish expert
    Rules out 1 from R4C5.
  15. Step 24 · Nice Loops/AICs expert
    Rules out 2 from R3C6.
  16. Step 25 · ALS-XZ expert
    Rules out 4 from R4C6.
  17. Step 26 · Nice Loops/AICs expert
    Rules out 1 from R6C4.
  18. Step 27 · Nice Loops/AICs expert
    Rules out 8 from R6C4.
  19. Step 29 · Skyscraper advanced
    Rules out 2 from R8C7.
  20. Step 30 · Nice Loops/AICs expert
    Rules out 4 from R7C6.
  21. Step 32 · Sue de Coq expert
    Rules out 1 from R8C6.
  22. Step 33 · ALS-XZ expert
    Rules out 9 from R4C9.
  23. Step 36 · Finned Fish expert
    Rules out 1 from R7C1.
  24. Step 43 · XY-Chain expert
    Rules out 1 from R7C5.

The book

Volume two: 150 new classic 9×9 grids, none repeated from book 1, ramping from hard to brutal.

150 new 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 Sudoku 1 · Extreme Killer Sudoku 1 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.