EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 74: 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 74 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
17 of 45 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), XY-Chain (×2), Cell Forcing Chains, Skyscraper, Sue de Coq, W-Wing, WXYZ-Wing, 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 (17)
  1. Step 6 · WXYZ-Wing expert
    Rules out 5 from R8C6.
  2. Step 8 · Nice Loops/AICs expert
    Rules out 1 from R1C4.
  3. Step 11 · Sue de Coq expert
    Rules out 3 from R1C1; 4 from R4C2; 8 from R4C2.
  4. Step 14 · ALS-XZ expert
    Rules out 8 from R1C3.
  5. Step 15 · Nice Loops/AICs expert
    Rules out 3 from R3C5.
  6. Step 16 · 2-String Kite advanced
    Rules out 3 from R2C9.
  7. Step 17 · ALS-XZ expert
    Rules out 1 from R9C5.
  8. Step 20 · XY-Chain expert
    Rules out 1 from R7C5.
  9. Step 22 · Skyscraper advanced
    Rules out 6 from R7C1, R8C6.
  10. Step 26 · XY-Chain expert
    Rules out 3 from R1C4, R2C2.
  11. Step 27 · ALS-XZ expert
    Rules out 8 from R1C8.
  12. Step 28 · Nice Loops/AICs expert
    Rules out 2 from R1C8.
  13. Step 31 · Nice Loops/AICs expert
    Rules out 3 from R2C4.
  14. Step 32 · Cell Forcing Chains expert
    Rules out 8 from R1C2.
  15. Step 36 · X-Wing/Swordfish advanced
    Rules out 3 from R7C4.
  16. Step 37 · 2-String Kite advanced
    Rules out 8 from R9C9.
  17. Step 40 · W-Wing advanced
    Rules out 7 from R9C9.

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.