EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 7: 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 7 of 150 in Extreme Sudoku 3
Difficulty
Expert 5 (expert and beyond), from the opening third of the book
Key technique
XY-Chain
Hard steps
17 of 38 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 (×3), Nice Loops/AICs (×2), WXYZ-Wing (×2), XY-Wing (×2), 2-String Kite, Finned Fish, Skyscraper.

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 (17)
  1. Step 5 · Finned Fish expert
    Rules out 6 from R6C1, R6C3.
  2. Step 6 · XY-Chain expert
    Rules out 4 from R2C5.
  3. Step 7 · WXYZ-Wing expert
    Rules out 4 from R9C6.
  4. Step 10 · WXYZ-Wing expert
    Rules out 2 from R1C9.
  5. Step 13 · Skyscraper advanced
    Rules out 3 from R5C4, R6C8, R6C9.
  6. Step 14 · 2-String Kite advanced
    Rules out 3 from R6C3.
  7. Step 16 · XY-Wing advanced
    Rules out 6 from R4C9, R5C1, R5C2.
  8. Step 17 · ALS-XZ expert
    Rules out 1 from R5C1, R6C1.
  9. Step 18 · ALS-XZ expert
    Rules out 6 from R4C1.
  10. Step 21 · ALS-XZ expert
    Rules out 3 from R4C9.
  11. Step 23 · Nice Loops/AICs expert
    Rules out 3 from R5C9.
  12. Step 24 · Nice Loops/AICs expert
    Rules out 5 from R6C3.
  13. Step 25 · XY-Wing advanced
    Rules out 5 from R8C2, R9C2.
  14. Step 26 · XY-Chain expert
    Rules out 3 from R1C3.
  15. Step 28 · XY-Chain expert
    Rules out 3 from R2C3, R3C4.
  16. Step 30 · XY-Chain expert
    Rules out 3 from R2C4, R6C6.
  17. Step 33 · XY-Chain expert
    Rules out 6 from R7C3.

The book

Volume three: 150 new classic 9×9 grids, none repeated from books 1 or 2, 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.

On Amazon from 8 Dec About the book

Try a free sample puzzle (PDF) · prints on A4 or US Letter

More step-by-step solutions: Extreme Sudoku 1 · Extreme Killer Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Killer Sudoku 3.