EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 83: 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 83 of 150 in Extreme Sudoku 2
Difficulty
Expert 7 (expert and beyond), from the middle third of the book
Key technique
Nice Loops/AICs
Hard steps
28 of 50 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 (×6), XY-Chain (×5), Finned Fish (×2), WXYZ-Wing (×2), 2-String Kite, Cell Forcing Chains, Sue de Coq, Unique Rectangles, X-Wing/Swordfish.

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 28)
  1. Step 5 · 2-String Kite advanced
    Rules out 5 from R9C8.
  2. Step 10 · Unique Rectangles advanced
    Rules out 3 from R3C3; 5 from R3C3.
  3. Step 11 · ALS-XZ expert
    Rules out 1 from R4C4, R5C3.
  4. Step 14 · ALS-XZ expert
    Rules out 4 from R2C9.
  5. Step 15 · ALS-XZ expert
    Rules out 2 from R5C3.
  6. Step 16 · WXYZ-Wing expert
    Rules out 2 from R4C7.
  7. Step 17 · Nice Loops/AICs expert
    Rules out 4 from R2C2.
  8. Step 18 · Nice Loops/AICs expert
    Rules out 8 from R2C3.
  9. Step 19 · ALS-XZ expert
    Rules out 2 from R3C1.
  10. Step 20 · ALS-XZ expert
    Rules out 2 from R8C3.
  11. Step 21 · Nice Loops/AICs expert
    Rules out 8 from R9C1.
  12. Step 22 · Nice Loops/AICs expert
    Rules out 6 from R5C3.
  13. Step 25 · ALS-XZ expert
    Rules out 8 from R6C9.
  14. Step 26 · Finned Fish expert
    Rules out 8 from R8C2.
  15. Step 28 · Nice Loops/AICs expert
    Rules out 2 from R5C7.
  16. Step 29 · Nice Loops/AICs expert
    Rules out 3 from R9C1.
  17. Step 30 · Nice Loops/AICs expert
    Rules out 9 from R9C2.
  18. Step 31 · Nice Loops/AICs expert
    Rules out 2 from R9C2.
  19. Step 32 · Cell Forcing Chains expert
    Rules out 3 from R1C3.
  20. Step 36 · WXYZ-Wing expert
    Rules out 9 from R7C7.
  21. Step 38 · Sue de Coq expert
    Rules out 2 from R7C2; 9 from R7C2.
  22. Step 39 · XY-Chain expert
    Rules out 8 from R9C2.
  23. Step 40 · XY-Chain expert
    Rules out 9 from R3C2.
  24. Step 41 · Finned Fish expert
    Rules out 9 from R6C9.

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.