EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 94: 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 94 of 150 in Extreme Sudoku 1
Difficulty
Expert 7 (expert and beyond), from the middle third of the book
Key technique
XY-Chain
Hard steps
21 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: ALS-XZ (×4), Nice Loops/AICs (×4), XY-Wing (×2), 2-String Kite, Cell Forcing Chains, Finned Fish, Sue de Coq, Unique Rectangles, 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 (21)
  1. Step 8 · 2-String Kite advanced
    Rules out 8 from R1C2.
  2. Step 9 · XY-Wing advanced
    Rules out 6 from R8C1.
  3. Step 10 · Finned Fish expert
    Rules out 6 from R7C4.
  4. Step 11 · XY-Chain expert
    Rules out 5 from R1C6.
  5. Step 12 · Sue de Coq expert
    Rules out 8 from R3C5; 5 from R7C4, R8C4; 6 from R8C4.
  6. Step 13 · ALS-XZ expert
    Rules out 6 from R7C5.
  7. Step 15 · ALS-XZ expert
    Rules out 5 from R5C5.
  8. Step 16 · Nice Loops/AICs expert
    Rules out 8 from R2C4.
  9. Step 17 · Nice Loops/AICs expert
    Rules out 8 from R1C8.
  10. Step 18 · ALS-XZ expert
    Rules out 1 from R3C8.
  11. Step 19 · ALS-XZ expert
    Rules out 5 from R3C7, R3C8.
  12. Step 20 · WXYZ-Wing expert
    Rules out 6 from R3C5.
  13. Step 23 · Nice Loops/AICs expert
    Rules out 6 from R7C8.
  14. Step 24 · Cell Forcing Chains expert
    Rules out 5 from R1C1, R1C2, R4C3, R5C4 and 2 more; 1 from R1C8, R4C4, R5C9; 3 from R1C9, R7C8.
  15. Step 27 · XY-Chain expert
    Rules out 5 from R7C2.
  16. Step 28 · Nice Loops/AICs expert
    Rules out 2 from R7C4.
  17. Step 30 · XY-Wing advanced
    Rules out 5 from R3C1, R9C2.
  18. Step 32 · Unique Rectangles advanced
    Rules out 3 from R7C2; 6 from R7C2.
  19. Step 35 · X-Wing/Swordfish advanced
    Rules out 8 from R4C4.
  20. Step 36 · XY-Chain expert
    Rules out 8 from R2C2.
  21. Step 38 · XY-Chain expert
    Rules out 8 from R1C6, R3C2.

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.