EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 3, puzzle 9: 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
Killer sudoku, number 9 of 150 in Extreme Killer Sudoku 3
Difficulty
Expert 4 (expert and beyond), from the opening third of the book
Key technique
Remote Pairs
Hard steps
14 of 90 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: Remote Pairs

A chain of cells that all hold the same pair alternates between the two digits. Cells that see both ends of an odd-length link cannot hold either digit.

Other advanced and expert techniques in this solve: Multi-Sector Locking (×3), 2-String Kite (×2), Advanced Innies (3+ sectors) (×2), XYZ-Wing (×2), Coloring/Multi-coloring, Finned Fish, Forcing Chains.

Every move above the basics is listed on the killer sudoku techniques page, each with a one-sentence explanation and worked examples from the books.

The hard steps, in text (14)
  1. Step 12 · Multi-Sector Locking advanced
    Rules out 9 from R1C4, R1C5; 6 from R1C7, R1C8, R2C7, R3C7; 8 from R1C8, R5C8.
  2. Step 14 · Advanced Innies (3+ sectors) advanced
    Rules out 5 from R2C5, R3C5, R5C5; 6 from R2C5, R3C5, R5C5; 7 from R2C5, R3C5, R4C5, R5C5.
  3. Step 22 · Multi-Sector Locking advanced
    Rules out 4 from R1C7, R1C8, R2C7.
  4. Step 23 · Advanced Innies (3+ sectors) advanced
    Rules out 5 from R4C8.
  5. Step 26 · Multi-Sector Locking advanced
    Rules out 5 from R1C7, R1C8, R2C7, R3C7.
  6. Step 34 · Remote Pairs expert
    Rules out 2 from R2C7; 3 from R2C7.
  7. Step 35 · Remote Pairs expert
    Rules out 5 from R1C5, R6C6; 6 from R6C6.
  8. Step 65 · 2-String Kite advanced
    Rules out 5 from R7C3.
  9. Step 66 · 2-String Kite advanced
    Rules out 7 from R7C3.
  10. Step 67 · Coloring/Multi-coloring expert
    Rules out 6 from R8C6.
  11. Step 68 · XYZ-Wing advanced
    Rules out 2 from R8C8.
  12. Step 69 · XYZ-Wing advanced
    Rules out 2 from R9C4.
  13. Step 71 · Finned Fish expert
    Rules out 7 from R7C2.
  14. Step 72 · Forcing Chains expert
    Rules out 8 from R1C4.

The book

Volume three: 150 new killers, none repeated from books 1 or 2. No starting digits, just cages and their totals, 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 15 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 Sudoku 3.