EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, 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 1
Difficulty
Expert 5 (expert and beyond), from the opening third of the book
Key technique
XY-Chain
Hard steps
23 of 48 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: XY-Chain

A chain of two-candidate cells, each linked to the next. Whichever way the start cell goes, one end of the chain holds the digit, so cells seeing both ends cannot.

Other advanced and expert techniques in this solve: ALS-XZ (×5), Nice Loops/AICs (×5), Finned Fish (×3), XY-Wing (×2), Empty Rectangle, WXYZ-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 (23)
  1. Step 4 · Finned Fish expert
    Rules out 5 from R1C6.
  2. Step 5 · Finned Fish expert
    Rules out 8 from R2C8.
  3. Step 6 · ALS-XZ expert
    Rules out 8 from R1C7.
  4. Step 9 · ALS-XZ expert
    Rules out 6 from R5C3.
  5. Step 10 · XY-Wing advanced
    Rules out 6 from R4C6.
  6. Step 13 · Empty Rectangle advanced
    Rules out 7 from R1C5.
  7. Step 14 · Finned Fish expert
    Rules out 6 from R1C9, R2C9.
  8. Step 15 · ALS-XZ expert
    Rules out 3 from R8C2.
  9. Step 16 · ALS-XZ expert
    Rules out 9 from R8C2.
  10. Step 17 · Nice Loops/AICs expert
    Rules out 8 from R9C6.
  11. Step 19 · Nice Loops/AICs expert
    Rules out 5 from R3C4.
  12. Step 20 · ALS-XZ expert
    Rules out 6 from R1C1.
  13. Step 21 · XY-Chain expert
    Rules out 3 from R9C1.
  14. Step 25 · XY-Chain expert
    Rules out 4 from R1C7.
  15. Step 27 · WXYZ-Wing expert
    Rules out 3 from R8C9.
  16. Step 29 · Nice Loops/AICs expert
    Rules out 7 from R1C9.
  17. Step 30 · XY-Chain expert
    Rules out 6 from R5C9.
  18. Step 31 · Nice Loops/AICs expert
    Rules out 6 from R2C3.
  19. Step 32 · Nice Loops/AICs expert
    Rules out 5 from R8C4.
  20. Step 35 · XY-Chain expert
    Rules out 6 from R3C2.
  21. Step 39 · XY-Chain expert
    Rules out 9 from R8C6.
  22. Step 40 · XY-Chain expert
    Rules out 9 from R7C6.
  23. Step 43 · XY-Wing advanced
    Rules out 5 from R9C3.

The book

Classic 9×9 sudoku with the warm-up taken out. Every grid sits at the top of the expert range or beyond it, and the book ramps from hard to brutal.

150 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 Killer Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.