EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, puzzle 110: 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 110 of 150 in Extreme Sudoku 1
Difficulty
Expert 5 (expert and beyond), from the final, hardest 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: Nice Loops/AICs (×5), 2-String Kite (×2), ALS-XZ, Cell Forcing Chains, Finned Fish, Skyscraper, X-Wing/Swordfish, XY-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 · Skyscraper advanced
    Rules out 8 from R5C9, R8C7.
  2. Step 8 · XY-Wing advanced
    Rules out 3 from R5C8, R8C9.
  3. Step 9 · ALS-XZ expert
    Rules out 5 from R1C7.
  4. Step 10 · Nice Loops/AICs expert
    Rules out 6 from R1C4.
  5. Step 11 · Nice Loops/AICs expert
    Rules out 1 from R6C3.
  6. Step 13 · Nice Loops/AICs expert
    Rules out 5 from R1C6.
  7. Step 14 · Nice Loops/AICs expert
    Rules out 5 from R2C7.
  8. Step 15 · XY-Chain expert
    Rules out 7 from R3C8, R5C7.
  9. Step 17 · 2-String Kite advanced
    Rules out 1 from R3C1.
  10. Step 18 · XY-Chain expert
    Rules out 5 from R3C7.
  11. Step 19 · Nice Loops/AICs expert
    Rules out 4 from R5C4.
  12. Step 20 · Cell Forcing Chains expert
    Rules out 5 from R2C5.
  13. Step 23 · Finned Fish expert
    Rules out 5 from R8C9.
  14. Step 26 · XY-Chain expert
    Rules out 8 from R9C1.
  15. Step 28 · XY-Chain expert
    Rules out 1 from R7C2.
  16. Step 30 · 2-String Kite advanced
    Rules out 7 from R1C6.
  17. Step 31 · XY-Chain expert
    Rules out 1 from R3C6.
  18. Step 32 · X-Wing/Swordfish advanced
    Rules out 1 from R1C2.
  19. Step 33 · XY-Chain expert
    Rules out 2 from R1C3.
  20. Step 35 · XY-Chain expert
    Rules out 6 from R1C7, R3C2.
  21. Step 40 · XY-Chain expert
    Rules out 1 from R3C2, R5C1.

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.