EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 142: 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 142 of 150 in Extreme Sudoku 2
Difficulty
Expert 6 (expert and beyond), from the final, hardest third of the book
Key technique
Nice Loops/AICs
Hard steps
29 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: ALS-XZ (×6), 2-String Kite (×3), Finned Fish (×3), XY-Chain (×3), Cell Forcing Chains, Sue de Coq, XY-Wing, 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 (24 of 29)
  1. Step 4 · Finned Fish expert
    Rules out 3 from R7C9.
  2. Step 5 · ALS-XZ expert
    Rules out 6 from R5C3, R6C3.
  3. Step 6 · 2-String Kite advanced
    Rules out 6 from R7C4.
  4. Step 7 · Finned Fish expert
    Rules out 6 from R7C9.
  5. Step 8 · ALS-XZ expert
    Rules out 5 from R9C4.
  6. Step 9 · Nice Loops/AICs expert
    Rules out 4 from R4C7.
  7. Step 11 · Nice Loops/AICs expert
    Rules out 8 from R7C9.
  8. Step 12 · Cell Forcing Chains expert
    Rules out 3 from R1C1.
  9. Step 16 · XYZ-Wing advanced
    Rules out 9 from R3C8.
  10. Step 17 · ALS-XZ expert
    Rules out 9 from R8C7, R8C9.
  11. Step 18 · Nice Loops/AICs expert
    Rules out 8 from R8C9.
  12. Step 19 · Nice Loops/AICs expert
    Rules out 8 from R6C6.
  13. Step 21 · Nice Loops/AICs expert
    Rules out 8 from R8C7.
  14. Step 24 · 2-String Kite advanced
    Rules out 9 from R7C6.
  15. Step 25 · Sue de Coq expert
    Rules out 9 from R9C7.
  16. Step 26 · ALS-XZ expert
    Rules out 2 from R2C7.
  17. Step 27 · Nice Loops/AICs expert
    Rules out 8 from R2C4.
  18. Step 28 · Nice Loops/AICs expert
    Rules out 2 from R2C2.
  19. Step 29 · Nice Loops/AICs expert
    Rules out 2 from R2C3.
  20. Step 31 · Nice Loops/AICs expert
    Rules out 8 from R3C4.
  21. Step 32 · Nice Loops/AICs expert
    Rules out 6 from R2C4.
  22. Step 33 · ALS-XZ expert
    Rules out 5 from R5C4.
  23. Step 35 · 2-String Kite advanced
    Rules out 2 from R9C5.
  24. Step 36 · Finned Fish expert
    Rules out 2 from R9C6.

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.