EXTREMEPUZZLE BOOKS

Extreme Sudoku 3, puzzle 149: 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 149 of 150 in Extreme Sudoku 3
Difficulty
Expert 7 (expert and beyond), from the final, hardest third of the book
Key technique
Nice Loops/AICs
Hard steps
31 of 57 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 (×7), 2-String Kite (×2), W-Wing (×2), WXYZ-Wing (×2), XY-Chain (×2), Cell Forcing Chains, Finned Fish, Sue de Coq, 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 (24 of 31)
  1. Step 5 · 2-String Kite advanced
    Rules out 3 from R9C1.
  2. Step 6 · 2-String Kite advanced
    Rules out 7 from R6C1.
  3. Step 7 · ALS-XZ expert
    Rules out 9 from R9C4.
  4. Step 8 · ALS-XZ expert
    Rules out 9 from R3C8.
  5. Step 9 · Cell Forcing Chains expert
    Rules out 5 from R1C2.
  6. Step 14 · W-Wing advanced
    Rules out 9 from R5C3.
  7. Step 15 · WXYZ-Wing expert
    Rules out 9 from R8C2, R8C3.
  8. Step 16 · Nice Loops/AICs expert
    Rules out 9 from R5C6.
  9. Step 17 · Nice Loops/AICs expert
    Rules out 9 from R8C8.
  10. Step 18 · Nice Loops/AICs expert
    Rules out 9 from R5C4.
  11. Step 19 · Nice Loops/AICs expert
    Rules out 4 from R4C1.
  12. Step 20 · WXYZ-Wing expert
    Rules out 9 from R4C9, R5C2.
  13. Step 21 · Nice Loops/AICs expert
    Rules out 3 from R5C1.
  14. Step 22 · W-Wing advanced
    Rules out 4 from R5C8.
  15. Step 24 · ALS-XZ expert
    Rules out 5 from R7C9.
  16. Step 25 · Nice Loops/AICs expert
    Rules out 4 from R5C3, R6C3, R8C1.
  17. Step 27 · ALS-XZ expert
    Rules out 6 from R6C4.
  18. Step 28 · Nice Loops/AICs expert
    Rules out 7 from R5C6.
  19. Step 29 · Nice Loops/AICs expert
    Rules out 5 from R2C8.
  20. Step 31 · Nice Loops/AICs expert
    Rules out 1 from R6C5.
  21. Step 33 · Nice Loops/AICs expert
    Rules out 9 from R2C6.
  22. Step 34 · Finned Fish expert
    Rules out 9 from R7C4.
  23. Step 36 · Sue de Coq expert
    Rules out 5 from R3C4.
  24. Step 37 · ALS-XZ expert
    Rules out 5 from R3C8.

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.