EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 93: 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 93 of 150 in Extreme Sudoku 2
Difficulty
Expert 5 (expert and beyond), from the middle third of the book
Key technique
Nice Loops/AICs
Hard steps
18 of 43 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), XY-Chain (×3), W-Wing (×2), Cell Forcing Chains, Finned Fish, Skyscraper.

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 4 · Skyscraper advanced
    Rules out 1 from R2C1.
  2. Step 6 · W-Wing advanced
    Rules out 4 from R2C7, R2C8, R3C6.
  3. Step 8 · Nice Loops/AICs expert
    Rules out 8 from R6C3, R7C1, R9C1.
  4. Step 10 · Nice Loops/AICs expert
    Rules out 8 from R3C3, R7C2, R9C2.
  5. Step 12 · Nice Loops/AICs expert
    Rules out 1 from R7C1.
  6. Step 13 · Nice Loops/AICs expert
    Rules out 9 from R8C6.
  7. Step 16 · ALS-XZ expert
    Rules out 4 from R9C9.
  8. Step 17 · ALS-XZ expert
    Rules out 2 from R9C9.
  9. Step 18 · Nice Loops/AICs expert
    Rules out 2 from R9C8.
  10. Step 19 · Cell Forcing Chains expert
    Rules out 9 from R1C7.
  11. Step 21 · W-Wing advanced
    Rules out 2 from R7C7.
  12. Step 22 · ALS-XZ expert
    Rules out 7 from R2C2.
  13. Step 23 · Nice Loops/AICs expert
    Rules out 9 from R6C8.
  14. Step 24 · Nice Loops/AICs expert
    Rules out 1 from R9C1.
  15. Step 27 · Finned Fish expert
    Rules out 2 from R9C6.
  16. Step 28 · XY-Chain expert
    Rules out 4 from R9C4.
  17. Step 34 · XY-Chain expert
    Rules out 9 from R1C2.
  18. Step 36 · XY-Chain expert
    Rules out 7 from R3C1, R9C2.

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.