EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 29: 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 29 of 150 in Extreme Sudoku 1
Difficulty
Expert 5 (expert and beyond), from the opening third of the book
Key technique
ALS-XZ
Hard steps
20 of 44 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: ALS-XZ

Two almost-locked sets (n cells with n+1 candidates) share a restricted digit X. Then a digit Z common to both must be in one of them, so cells seeing all of its copies cannot be Z.

Other advanced and expert techniques in this solve: Nice Loops/AICs (×5), Finned Fish (×2), XY-Chain (×2), Empty Rectangle, Skyscraper, WXYZ-Wing, X-Wing/Swordfish, XY-Wing, XYZ-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 (20)
  1. Step 4 · Empty Rectangle advanced
    Rules out 5 from R5C9.
  2. Step 5 · XY-Wing advanced
    Rules out 3 from R1C9, R5C8, R6C8.
  3. Step 6 · Finned Fish expert
    Rules out 3 from R1C4, R1C5.
  4. Step 7 · ALS-XZ expert
    Rules out 8 from R7C2, R8C2.
  5. Step 8 · ALS-XZ expert
    Rules out 1 from R3C3, R4C2.
  6. Step 9 · ALS-XZ expert
    Rules out 3 from R5C9, R6C4.
  7. Step 14 · XY-Chain expert
    Rules out 2 from R3C7.
  8. Step 18 · WXYZ-Wing expert
    Rules out 4 from R4C8.
  9. Step 19 · Skyscraper advanced
    Rules out 4 from R5C4, R7C5.
  10. Step 21 · ALS-XZ expert
    Rules out 5 from R1C4.
  11. Step 22 · Nice Loops/AICs expert
    Rules out 3 from R3C7, R7C8.
  12. Step 24 · Nice Loops/AICs expert
    Rules out 9 from R4C2.
  13. Step 26 · ALS-XZ expert
    Rules out 5 from R4C9.
  14. Step 27 · Nice Loops/AICs expert
    Rules out 9 from R5C2.
  15. Step 29 · Nice Loops/AICs expert
    Rules out 1 from R1C1.
  16. Step 33 · Finned Fish expert
    Rules out 6 from R3C4.
  17. Step 35 · XYZ-Wing advanced
    Rules out 3 from R7C5.
  18. Step 36 · Nice Loops/AICs expert
    Rules out 6 from R4C9.
  19. Step 37 · X-Wing/Swordfish advanced
    Rules out 6 from R1C6.
  20. Step 40 · XY-Chain expert
    Rules out 6 from R3C6, R9C4.

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.

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