EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 28: 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 28 of 150 in Extreme Sudoku 2
Difficulty
Expert 6 (expert and beyond), from the opening 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 (×4), ALS-XZ (×2), W-Wing (×2), WXYZ-Wing (×2), XY-Wing (×2), Cell Forcing Chains, Sue de Coq.

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 7 · XY-Chain expert
    Rules out 6 from R7C4.
  2. Step 8 · WXYZ-Wing expert
    Rules out 3 from R2C4.
  3. Step 9 · ALS-XZ expert
    Rules out 5 from R2C5.
  4. Step 12 · ALS-XZ expert
    Rules out 1 from R8C2.
  5. Step 13 · Nice Loops/AICs expert
    Rules out 1 from R8C8.
  6. Step 14 · Nice Loops/AICs expert
    Rules out 4 from R3C2, R3C7.
  7. Step 17 · WXYZ-Wing expert
    Rules out 3 from R8C7.
  8. Step 18 · Nice Loops/AICs expert
    Rules out 4 from R1C9.
  9. Step 19 · Nice Loops/AICs expert
    Rules out 2 from R2C5.
  10. Step 22 · Cell Forcing Chains expert
    Rules out 3 from R1C6.
  11. Step 28 · W-Wing advanced
    Rules out 3 from R7C9.
  12. Step 29 · W-Wing advanced
    Rules out 7 from R6C9.
  13. Step 30 · XY-Chain expert
    Rules out 6 from R6C1, R9C2.
  14. Step 31 · XY-Wing advanced
    Rules out 6 from R2C2.
  15. Step 33 · XY-Chain expert
    Rules out 6 from R4C7.
  16. Step 36 · Sue de Coq expert
    Rules out 4 from R5C3, R6C3; 3 from R8C2.
  17. Step 37 · XY-Chain expert
    Rules out 2 from R5C2.
  18. Step 39 · XY-Wing advanced
    Rules out 3 from R9C2.

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.

Buy on Amazon US Buy on Amazon UK
Other Amazon stores
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 Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.