EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 11: 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 11 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
15 of 35 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 (×3), Finned Fish (×2), XY-Chain (×2), 2-String Kite, 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 (15)
  1. Step 6 · 2-String Kite advanced
    Rules out 7 from R6C8.
  2. Step 7 · ALS-XZ expert
    Rules out 3 from R3C2.
  3. Step 9 · ALS-XZ expert
    Rules out 3 from R1C3.
  4. Step 11 · Nice Loops/AICs expert
    Rules out 4 from R1C1.
  5. Step 15 · Sue de Coq expert
    Rules out 3 from R9C9; 7 from R9C9.
  6. Step 16 · Finned Fish expert
    Rules out 7 from R6C7.
  7. Step 17 · ALS-XZ expert
    Rules out 5 from R1C2, R9C1.
  8. Step 19 · ALS-XZ expert
    Rules out 3 from R6C1.
  9. Step 20 · ALS-XZ expert
    Rules out 2 from R9C3.
  10. Step 21 · Nice Loops/AICs expert
    Rules out 9 from R9C4.
  11. Step 23 · Nice Loops/AICs expert
    Rules out 7 from R3C1, R5C3.
  12. Step 25 · ALS-XZ expert
    Rules out 8 from R3C3, R4C1.
  13. Step 29 · Finned Fish expert
    Rules out 3 from R9C8.
  14. Step 30 · XY-Chain expert
    Rules out 7 from R7C8.
  15. Step 32 · XY-Chain expert
    Rules out 6 from R7C8.

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.