EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 3, puzzle 108: 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 108 of 150 in Extreme Killer Sudoku 3
Difficulty
Expert 2 (expert and beyond), from the final, hardest third of the book
Key technique
Remote Pairs
Hard steps
8 of 84 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 (×2), XY-Wing (×2), Advanced Innies (3+ sectors), Forcing Chains, XYZ-Wing.

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 (8)
  1. Step 6 · Multi-Sector Locking advanced
    Rules out 1 from R7C9, R8C7, R8C8, R8C9 and 5 more.
  2. Step 7 · Advanced Innies (3+ sectors) advanced
    Places 8 in R5C4 and rules out 2 from R1C3, R2C3, R4C3, R5C1 and 2 more; 8 from R1C4, R2C4, R2C5, R3C4 and 13 more; 3 from R2C5, R6C5, R8C5.
  3. Step 18 · Multi-Sector Locking advanced
    Rules out 8 from R1C1, R2C1, R3C1, R3C2 and 2 more; 9 from R1C4, R2C4; 1 from R7C6, R8C6.
  4. Step 65 · XYZ-Wing advanced
    Rules out 3 from R2C7.
  5. Step 66 · Remote Pairs expert
    Rules out 7 from R3C7; 8 from R3C7.
  6. Step 68 · XY-Wing advanced
    Rules out 8 from R2C7, R2C8.
  7. Step 72 · XY-Wing advanced
    Rules out 8 from R1C9, R6C8, R7C8.
  8. Step 73 · Forcing Chains expert
    Rules out 7 from R1C1.

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.