EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 93: 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 93 of 150 in Extreme Sudoku 1
Difficulty
Expert 7 (expert and beyond), from the middle third of the book
Key technique
ALS-XZ
Hard steps
13 of 27 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: XY-Chain (×2), Cell Forcing Chains, Finned Fish, Nice Loops/AICs, Sue de Coq, W-Wing, WXYZ-Wing, X-Wing/Swordfish.

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 (13)
  1. Step 5 · X-Wing/Swordfish advanced
    Rules out 7 from R4C9.
  2. Step 6 · WXYZ-Wing expert
    Rules out 8 from R5C9.
  3. Step 7 · Finned Fish expert
    Rules out 8 from R4C3, R6C3.
  4. Step 8 · ALS-XZ expert
    Rules out 1 from R5C3.
  5. Step 11 · ALS-XZ expert
    Rules out 2 from R1C4.
  6. Step 12 · ALS-XZ expert
    Rules out 9 from R5C1.
  7. Step 13 · ALS-XZ expert
    Rules out 9 from R2C4.
  8. Step 14 · Nice Loops/AICs expert
    Rules out 5 from R1C3.
  9. Step 15 · Cell Forcing Chains expert
    Rules out 5 from R1C1, R5C8, R6C3.
  10. Step 16 · Sue de Coq expert
    Rules out 3 from R4C7, R4C8; 9 from R5C3.
  11. Step 17 · XY-Chain expert
    Rules out 3 from R9C8.
  12. Step 23 · XY-Chain expert
    Rules out 8 from R1C3, R1C4.
  13. Step 24 · W-Wing advanced
    Rules out 2 from R1C8.

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.