EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 102: 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 102 of 150 in Extreme Sudoku 3
Difficulty
Expert 6 (expert and beyond), from the final, hardest third of the book
Key technique
Nice Loops/AICs
Hard steps
29 of 52 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: Nice Loops/AICs

An alternating chain of strong and weak links. Whichever end is true, the conclusion holds, so the digit at the marked cell is ruled out.

Other advanced and expert techniques in this solve: ALS-XZ (×6), XY-Chain (×5), Finned Fish (×2), 2-String Kite, Cell Forcing Chains, Empty Rectangle, 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 (24 of 29)
  1. Step 7 · Finned Fish expert
    Rules out 5 from R8C1, R9C1.
  2. Step 8 · ALS-XZ expert
    Rules out 8 from R6C1.
  3. Step 9 · Nice Loops/AICs expert
    Rules out 7 from R2C2.
  4. Step 11 · W-Wing advanced
    Rules out 4 from R2C4, R2C5, R3C1.
  5. Step 13 · Nice Loops/AICs expert
    Rules out 7 from R7C2.
  6. Step 14 · Nice Loops/AICs expert
    Rules out 5 from R7C1.
  7. Step 15 · Cell Forcing Chains expert
    Rules out 8 from R1C7, R1C9, R2C4, R2C5 and 1 more; 1 from R4C1, R4C7, R4C9, R9C4; 7 from R4C7, R4C9, R6C1, R6C3.
  8. Step 16 · Empty Rectangle advanced
    Rules out 1 from R8C1.
  9. Step 18 · ALS-XZ expert
    Rules out 9 from R1C1, R3C1.
  10. Step 19 · Nice Loops/AICs expert
    Rules out 5 from R1C3.
  11. Step 20 · Nice Loops/AICs expert
    Rules out 6 from R3C5.
  12. Step 21 · Nice Loops/AICs expert
    Rules out 5 from R8C7.
  13. Step 22 · Nice Loops/AICs expert
    Rules out 5 from R1C1, R1C2, R3C9.
  14. Step 24 · XY-Chain expert
    Rules out 9 from R1C3.
  15. Step 25 · XY-Chain expert
    Rules out 7 from R1C1.
  16. Step 26 · ALS-XZ expert
    Rules out 6 from R1C7.
  17. Step 28 · ALS-XZ expert
    Rules out 3 from R4C1.
  18. Step 31 · XY-Chain expert
    Rules out 9 from R7C3.
  19. Step 32 · XY-Chain expert
    Rules out 8 from R5C1.
  20. Step 33 · WXYZ-Wing expert
    Rules out 7 from R2C8.
  21. Step 35 · ALS-XZ expert
    Rules out 7 from R7C9.
  22. Step 36 · ALS-XZ expert
    Rules out 1 from R7C1.
  23. Step 37 · Finned Fish expert
    Rules out 1 from R9C9.
  24. Step 38 · Nice Loops/AICs expert
    Rules out 6 from R7C9.

The book

Volume three: 150 new classic 9×9 grids, none repeated from books 1 or 2, ramping from hard to brutal.

150 new 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.

On Amazon from 8 Dec About the book

Try a free sample puzzle (PDF) · prints on A4 or US Letter

More step-by-step solutions: Extreme Sudoku 1 · Extreme Killer Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Killer Sudoku 3.