EXTREMEPUZZLE BOOKS

Extreme Sudoku 1, 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 1
Difficulty
Expert 7 (expert and beyond), from the final, hardest third of the book
Key technique
Nice Loops/AICs
Hard steps
23 of 47 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 (×4), WXYZ-Wing (×2), Cell Forcing Chains, Finned Fish, Sue de Coq, W-Wing, XY-Chain.

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 (23)
  1. Step 4 · ALS-XZ expert
    Rules out 9 from R2C5.
  2. Step 5 · Nice Loops/AICs expert
    Rules out 6 from R2C6.
  3. Step 6 · Nice Loops/AICs expert
    Rules out 6 from R2C5.
  4. Step 7 · Nice Loops/AICs expert
    Rules out 6 from R9C5.
  5. Step 8 · Nice Loops/AICs expert
    Rules out 9 from R9C5.
  6. Step 9 · Nice Loops/AICs expert
    Rules out 7 from R6C2.
  7. Step 10 · Nice Loops/AICs expert
    Rules out 2 from R9C5.
  8. Step 11 · Nice Loops/AICs expert
    Rules out 9 from R9C6.
  9. Step 12 · Nice Loops/AICs expert
    Rules out 9 from R2C6.
  10. Step 13 · Nice Loops/AICs expert
    Rules out 4 from R2C5.
  11. Step 15 · WXYZ-Wing expert
    Rules out 9 from R7C6.
  12. Step 16 · ALS-XZ expert
    Rules out 6 from R7C7, R7C9.
  13. Step 17 · Nice Loops/AICs expert
    Rules out 2 from R2C6.
  14. Step 18 · Nice Loops/AICs expert
    Rules out 3 from R7C2.
  15. Step 19 · Cell Forcing Chains expert
    Rules out 2 from R2C5.
  16. Step 24 · Finned Fish expert
    Rules out 9 from R7C2.
  17. Step 25 · WXYZ-Wing expert
    Rules out 6 from R3C7, R3C8.
  18. Step 27 · ALS-XZ expert
    Rules out 3 from R7C7.
  19. Step 29 · W-Wing advanced
    Rules out 9 from R1C2.
  20. Step 30 · Sue de Coq expert
    Rules out 1 from R6C7; 9 from R9C7.
  21. Step 31 · ALS-XZ expert
    Rules out 4 from R3C7.
  22. Step 34 · Nice Loops/AICs expert
    Rules out 9 from R6C1.
  23. Step 36 · XY-Chain expert
    Rules out 9 from R7C5.

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.

Buy on Amazon US Buy on Amazon UK
Other Amazon stores
About the book

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

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