EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 71: 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 71 of 150 in Extreme Sudoku 1
Difficulty
Expert 5 (expert and beyond), from the middle third of the book
Key technique
XY-Chain
Hard steps
21 of 49 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 (×5), Nice Loops/AICs (×3), XYZ-Wing (×2), Finned Fish, Skyscraper, W-Wing, WXYZ-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 (21)
  1. Step 7 · Finned Fish expert
    Rules out 4 from R6C8.
  2. Step 9 · ALS-XZ expert
    Rules out 7 from R5C3, R6C3.
  3. Step 10 · ALS-XZ expert
    Rules out 2 from R4C8, R4C9.
  4. Step 11 · Nice Loops/AICs expert
    Rules out 1 from R2C8.
  5. Step 12 · Nice Loops/AICs expert
    Rules out 4 from R3C5.
  6. Step 13 · Nice Loops/AICs expert
    Rules out 3 from R4C2, R6C2, R9C2.
  7. Step 17 · ALS-XZ expert
    Rules out 3 from R8C2.
  8. Step 23 · XY-Chain expert
    Rules out 2 from R8C6, R9C9.
  9. Step 25 · ALS-XZ expert
    Rules out 8 from R4C5.
  10. Step 27 · XYZ-Wing advanced
    Rules out 7 from R6C4.
  11. Step 28 · ALS-XZ expert
    Rules out 8 from R8C8.
  12. Step 29 · WXYZ-Wing expert
    Rules out 8 from R1C9, R3C9.
  13. Step 31 · XY-Chain expert
    Rules out 2 from R8C8.
  14. Step 32 · XY-Chain expert
    Rules out 2 from R8C9.
  15. Step 35 · XYZ-Wing advanced
    Rules out 7 from R5C5.
  16. Step 36 · W-Wing advanced
    Rules out 8 from R6C4.
  17. Step 37 · XY-Chain expert
    Rules out 7 from R5C4.
  18. Step 40 · XY-Chain expert
    Rules out 7 from R4C1.
  19. Step 41 · XY-Chain expert
    Rules out 5 from R6C5.
  20. Step 43 · XY-Chain expert
    Rules out 1 from R9C3.
  21. Step 45 · Skyscraper advanced
    Rules out 3 from R5C9, R6C5.

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.