EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 2, puzzle 107: 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 107 of 150 in Extreme Killer Sudoku 2
Difficulty
Expert 2 (expert and beyond), from the final, hardest third of the book
Key technique
Forcing Chains
Hard steps
11 of 80 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: Forcing Chains

Try each candidate of one cell in turn. Every choice leads to the same result, so that result must be true.

Other advanced and expert techniques in this solve: Multi-Sector Locking (×3), Advanced Innies (3+ sectors) (×2), 2-String Kite, Empty Rectangle, Remote Pairs, Skyscraper, 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 (11)
  1. Step 11 · Multi-Sector Locking advanced
    Rules out 9 from R4C1, R4C4, R4C6, R5C3 and 2 more.
  2. Step 13 · Advanced Innies (3+ sectors) advanced
    Rules out 1 from R2C5.
  3. Step 14 · Forcing Chains expert
    Rules out 4 from R3C1; 6 from R3C1.
  4. Step 41 · XYZ-Wing advanced
    Rules out 3 from R2C6.
  5. Step 42 · 2-String Kite advanced
    Rules out 1 from R9C2.
  6. Step 43 · Multi-Sector Locking advanced
    Rules out 4 from R7C3; 6 from R8C6.
  7. Step 44 · Advanced Innies (3+ sectors) advanced
    Rules out 7 from R6C2; 3 from R6C4.
  8. Step 54 · Empty Rectangle advanced
    Rules out 1 from R6C3.
  9. Step 55 · Multi-Sector Locking advanced
    Rules out 8 from R8C6.
  10. Step 56 · Remote Pairs expert
    Rules out 6 from R2C6.
  11. Step 63 · Skyscraper advanced
    Rules out 4 from R4C5, R4C6.

The book

Volume two: 150 new killers, none repeated from book 1. 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.

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