EXTREMEPUZZLE BOOKS

Extreme Sudoku 2, puzzle 122: 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 122 of 150 in Extreme Sudoku 2
Difficulty
Expert 7 (expert and beyond), from the final, hardest third of the book
Key technique
Nice Loops/AICs
Hard steps
18 of 44 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 (×3), 2-String Kite, Cell Forcing Chains, Finned Fish, Skyscraper, Sue de Coq, W-Wing, WXYZ-Wing, XY-Chain, XY-Wing, XYZ-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 (18)
  1. Step 3 · 2-String Kite advanced
    Rules out 7 from R1C5.
  2. Step 4 · Finned Fish expert
    Rules out 4 from R3C6.
  3. Step 5 · ALS-XZ expert
    Rules out 6 from R7C6.
  4. Step 6 · Skyscraper advanced
    Rules out 6 from R9C9.
  5. Step 8 · ALS-XZ expert
    Rules out 6 from R2C4, R9C5.
  6. Step 10 · Nice Loops/AICs expert
    Rules out 7 from R3C1.
  7. Step 11 · Nice Loops/AICs expert
    Rules out 7 from R3C9.
  8. Step 12 · Nice Loops/AICs expert
    Rules out 7 from R4C5, R4C6, R6C9.
  9. Step 14 · Nice Loops/AICs expert
    Rules out 8 from R7C8.
  10. Step 15 · ALS-XZ expert
    Rules out 8 from R4C7.
  11. Step 16 · Nice Loops/AICs expert
    Rules out 5 from R7C8.
  12. Step 17 · Cell Forcing Chains expert
    Rules out 2 from R2C4.
  13. Step 20 · Sue de Coq expert
    Rules out 1 from R4C6, R5C6; 4 from R9C4; 6 from R9C4.
  14. Step 21 · XY-Chain expert
    Rules out 5 from R7C7, R7C9.
  15. Step 24 · WXYZ-Wing expert
    Rules out 3 from R4C2, R4C3.
  16. Step 29 · XYZ-Wing advanced
    Rules out 2 from R3C1.
  17. Step 30 · W-Wing advanced
    Rules out 8 from R1C1, R3C9.
  18. Step 32 · XY-Wing advanced
    Rules out 6 from R4C6, R6C9.

The book

Volume two: 150 new classic 9×9 grids, none repeated from book 1, 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.

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 Sudoku 1 · Extreme Killer Sudoku 1 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.