EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 109: 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 109 of 150 in Extreme Sudoku 1
Difficulty
Expert 5 (expert and beyond), from the final, hardest third of the book
Key technique
XY-Chain
Hard steps
18 of 43 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: Nice Loops/AICs (×5), ALS-XZ (×3), 2-String Kite, Cell Forcing Chains, 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 (18)
  1. Step 5 · 2-String Kite advanced
    Rules out 9 from R8C6.
  2. Step 6 · XY-Chain expert
    Rules out 4 from R1C7, R2C7.
  3. Step 8 · XY-Chain expert
    Rules out 6 from R3C2.
  4. Step 9 · WXYZ-Wing expert
    Rules out 6 from R8C3.
  5. Step 10 · ALS-XZ expert
    Rules out 2 from R9C3.
  6. Step 11 · Nice Loops/AICs expert
    Rules out 6 from R5C2.
  7. Step 12 · Cell Forcing Chains expert
    Rules out 6 from R1C7.
  8. Step 15 · XY-Chain expert
    Rules out 6 from R8C1.
  9. Step 17 · ALS-XZ expert
    Rules out 8 from R3C2.
  10. Step 18 · Nice Loops/AICs expert
    Rules out 6 from R3C1.
  11. Step 19 · Nice Loops/AICs expert
    Rules out 1 from R7C3.
  12. Step 25 · ALS-XZ expert
    Rules out 8 from R4C3, R5C3.
  13. Step 26 · Nice Loops/AICs expert
    Rules out 6 from R5C1.
  14. Step 27 · Nice Loops/AICs expert
    Rules out 6 from R2C7.
  15. Step 30 · XY-Chain expert
    Rules out 3 from R9C2.
  16. Step 31 · XY-Chain expert
    Rules out 5 from R3C8.
  17. Step 35 · XY-Chain expert
    Rules out 7 from R4C1, R5C4.
  18. Step 39 · XY-Chain expert
    Rules out 8 from R4C1.

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.