EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 136: 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 136 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
22 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 (×3), ALS-XZ (×2), Empty Rectangle (×2), Finned Fish (×2), XYZ-Wing (×2), 2-String Kite, Cell Forcing Chains, W-Wing, WXYZ-Wing, XY-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 (22)
  1. Step 4 · 2-String Kite advanced
    Rules out 1 from R4C5.
  2. Step 5 · Empty Rectangle advanced
    Rules out 8 from R4C6.
  3. Step 6 · Finned Fish expert
    Rules out 8 from R4C5.
  4. Step 7 · Nice Loops/AICs expert
    Rules out 8 from R3C6.
  5. Step 8 · Cell Forcing Chains expert
    Rules out 1 from R1C3.
  6. Step 10 · ALS-XZ expert
    Rules out 8 from R6C8.
  7. Step 11 · Nice Loops/AICs expert
    Rules out 2 from R3C1.
  8. Step 13 · Nice Loops/AICs expert
    Rules out 1 from R1C2, R2C6.
  9. Step 15 · Nice Loops/AICs expert
    Rules out 1 from R4C3.
  10. Step 18 · ALS-XZ expert
    Rules out 7 from R7C8.
  11. Step 19 · Finned Fish expert
    Rules out 7 from R5C7.
  12. Step 20 · WXYZ-Wing expert
    Rules out 8 from R5C8.
  13. Step 22 · Nice Loops/AICs expert
    Rules out 8 from R5C6, R6C6.
  14. Step 23 · Nice Loops/AICs expert
    Rules out 8 from R3C1.
  15. Step 24 · XYZ-Wing advanced
    Rules out 3 from R2C2.
  16. Step 26 · XY-Chain expert
    Rules out 7 from R9C7.
  17. Step 27 · XY-Chain expert
    Rules out 7 from R5C1, R9C8.
  18. Step 31 · Empty Rectangle advanced
    Rules out 8 from R5C4.
  19. Step 33 · XY-Chain expert
    Rules out 6 from R4C8, R5C8, R8C7.
  20. Step 39 · XY-Wing advanced
    Rules out 9 from R5C1.
  21. Step 42 · XYZ-Wing advanced
    Rules out 9 from R4C4.
  22. Step 44 · W-Wing advanced
    Rules out 5 from R4C4, R6C4, R8C6.

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.