EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 89: 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 89 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
23 of 49 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: XY-Chain (×4), ALS-XZ (×2), XY-Wing (×2), Cell Forcing Chains, Finned Fish, Sue de Coq, Unique Rectangles, WXYZ-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 (23)
  1. Step 6 · Finned Fish expert
    Rules out 5 from R4C1.
  2. Step 7 · Sue de Coq expert
    Rules out 4 from R1C4; 6 from R1C4, R2C6; 7 from R5C5, R9C5.
  3. Step 8 · Nice Loops/AICs expert
    Rules out 9 from R4C4.
  4. Step 10 · ALS-XZ expert
    Rules out 1 from R6C2.
  5. Step 11 · Nice Loops/AICs expert
    Rules out 6 from R3C5.
  6. Step 12 · Nice Loops/AICs expert
    Rules out 8 from R4C6.
  7. Step 13 · Nice Loops/AICs expert
    Rules out 5 from R7C2.
  8. Step 14 · Nice Loops/AICs expert
    Rules out 5 from R2C2.
  9. Step 15 · Nice Loops/AICs expert
    Rules out 6 from R3C2.
  10. Step 16 · Nice Loops/AICs expert
    Rules out 4 from R2C2.
  11. Step 17 · Cell Forcing Chains expert
    Rules out 9 from R2C2.
  12. Step 19 · Nice Loops/AICs expert
    Rules out 5 from R4C7.
  13. Step 20 · Nice Loops/AICs expert
    Rules out 6 from R3C7.
  14. Step 24 · ALS-XZ expert
    Rules out 5 from R5C1, R5C2.
  15. Step 27 · WXYZ-Wing expert
    Rules out 1 from R1C2, R3C2.
  16. Step 29 · Nice Loops/AICs expert
    Rules out 3 from R4C1.
  17. Step 30 · XY-Wing advanced
    Rules out 1 from R4C8.
  18. Step 36 · XY-Wing advanced
    Rules out 3 from R1C9.
  19. Step 37 · Unique Rectangles advanced
    Rules out 4 from R1C3; 7 from R1C3.
  20. Step 40 · XY-Chain expert
    Rules out 8 from R6C4.
  21. Step 41 · XY-Chain expert
    Rules out 4 from R3C2.
  22. Step 43 · XY-Chain expert
    Rules out 9 from R1C2.
  23. Step 46 · XY-Chain expert
    Rules out 4 from R1C2.

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.