EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 26: 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 26 of 150 in Extreme Sudoku 2
Difficulty
Expert 6 (expert and beyond), from the opening third of the book
Key technique
Nice Loops/AICs
Hard steps
19 of 47 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 (×5), XY-Chain (×2), Cell Forcing Chains, Empty Rectangle, Finned Fish, W-Wing, WXYZ-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 (19)
  1. Step 5 · Finned Fish expert
    Rules out 5 from R8C8.
  2. Step 7 · ALS-XZ expert
    Rules out 1 from R8C2.
  3. Step 8 · ALS-XZ expert
    Rules out 1 from R2C8.
  4. Step 9 · ALS-XZ expert
    Rules out 6 from R5C5.
  5. Step 10 · Empty Rectangle advanced
    Rules out 6 from R2C4.
  6. Step 11 · ALS-XZ expert
    Rules out 4 from R2C4, R2C6.
  7. Step 12 · Nice Loops/AICs expert
    Rules out 1 from R3C8.
  8. Step 13 · Nice Loops/AICs expert
    Rules out 9 from R7C9.
  9. Step 14 · Nice Loops/AICs expert
    Rules out 3 from R8C3.
  10. Step 16 · Cell Forcing Chains expert
    Rules out 1 from R2C1.
  11. Step 19 · Nice Loops/AICs expert
    Rules out 6 from R5C8.
  12. Step 21 · Nice Loops/AICs expert
    Rules out 6 from R2C9.
  13. Step 25 · XYZ-Wing advanced
    Rules out 4 from R7C7.
  14. Step 26 · WXYZ-Wing expert
    Rules out 6 from R1C5, R2C8.
  15. Step 28 · ALS-XZ expert
    Rules out 3 from R2C6.
  16. Step 29 · Nice Loops/AICs expert
    Rules out 3 from R2C4.
  17. Step 32 · XY-Chain expert
    Rules out 1 from R3C2.
  18. Step 36 · W-Wing advanced
    Rules out 9 from R6C7, R6C8.
  19. Step 37 · XY-Chain expert
    Rules out 3 from R1C5.

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.