EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 82: 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 82 of 150 in Extreme Sudoku 1
Difficulty
Expert 6 (expert and beyond), from the middle third of the book
Key technique
Nice Loops/AICs
Hard steps
19 of 39 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 (×3), 2-String Kite (×2), Skyscraper (×2), XY-Wing (×2), Cell Forcing Chains, Sue de Coq, W-Wing, WXYZ-Wing, XY-Chain, 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 (19)
  1. Step 5 · 2-String Kite advanced
    Rules out 6 from R8C8.
  2. Step 6 · WXYZ-Wing expert
    Rules out 9 from R3C4.
  3. Step 7 · Sue de Coq expert
    Rules out 5 from R4C7, R7C9; 6 from R4C7; 9 from R9C8.
  4. Step 8 · ALS-XZ expert
    Rules out 2 from R9C1.
  5. Step 9 · ALS-XZ expert
    Rules out 7 from R4C4, R6C8.
  6. Step 11 · Nice Loops/AICs expert
    Rules out 8 from R5C9.
  7. Step 14 · XYZ-Wing advanced
    Rules out 9 from R2C5.
  8. Step 15 · ALS-XZ expert
    Rules out 9 from R8C5.
  9. Step 16 · Nice Loops/AICs expert
    Rules out 9 from R6C3.
  10. Step 17 · Nice Loops/AICs expert
    Rules out 5 from R6C2.
  11. Step 18 · Cell Forcing Chains expert
    Rules out 6 from R2C6.
  12. Step 21 · W-Wing advanced
    Rules out 1 from R6C1, R7C2.
  13. Step 23 · Nice Loops/AICs expert
    Rules out 9 from R4C1, R4C2, R4C3.
  14. Step 26 · Skyscraper advanced
    Rules out 2 from R4C4, R5C1.
  15. Step 28 · XY-Chain expert
    Rules out 4 from R3C8.
  16. Step 30 · 2-String Kite advanced
    Rules out 5 from R4C1.
  17. Step 31 · XY-Wing advanced
    Rules out 6 from R6C8.
  18. Step 33 · Skyscraper advanced
    Rules out 5 from R2C3.
  19. Step 35 · XY-Wing advanced
    Rules out 9 from R4C7, R8C8.

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.