EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 68: 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 68 of 150 in Extreme Sudoku 3
Difficulty
Expert 7 (expert and beyond), from the middle 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 (×3), XY-Wing (×3), WXYZ-Wing (×2), 2-String Kite, ALS-XZ, Cell Forcing Chains, Finned Fish, 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 6 · WXYZ-Wing expert
    Rules out 2 from R7C4, R8C4.
  2. Step 7 · Nice Loops/AICs expert
    Rules out 5 from R2C9.
  3. Step 8 · Nice Loops/AICs expert
    Rules out 9 from R4C2, R6C6.
  4. Step 11 · WXYZ-Wing expert
    Rules out 6 from R1C2.
  5. Step 12 · Nice Loops/AICs expert
    Rules out 1 from R6C3.
  6. Step 13 · Cell Forcing Chains expert
    Rules out 5 from R1C1.
  7. Step 16 · Sue de Coq expert
    Rules out 7 from R2C9; 8 from R3C8.
  8. Step 17 · XY-Wing advanced
    Rules out 6 from R4C8.
  9. Step 18 · XY-Chain expert
    Rules out 6 from R7C8, R9C8.
  10. Step 26 · 2-String Kite advanced
    Rules out 2 from R9C6.
  11. Step 27 · XY-Wing advanced
    Rules out 6 from R9C3.
  12. Step 29 · Finned Fish expert
    Rules out 2 from R9C4.
  13. Step 31 · XY-Chain expert
    Rules out 7 from R1C9.
  14. Step 32 · XY-Chain expert
    Rules out 7 from R4C7.
  15. Step 33 · XY-Chain expert
    Rules out 1 from R8C2.
  16. Step 34 · ALS-XZ expert
    Rules out 7 from R9C2.
  17. Step 35 · XY-Chain expert
    Rules out 5 from R1C7.
  18. Step 37 · XY-Wing advanced
    Rules out 2 from R1C5, R2C9.

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.