EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 3, puzzle 42: 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 42 of 150 in Extreme Killer Sudoku 3
Difficulty
Expert 3 (expert and beyond), from the opening third of the book
Key technique
Coloring/Multi-coloring
Hard steps
9 of 71 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: Coloring/Multi-coloring

Following one digit’s strong links, cells get two colours: one colour is true and the other is false. A cell that sees both colours cannot hold the digit.

Other advanced and expert techniques in this solve: Advanced Innies (3+ sectors) (×4), 2-String Kite, Finned Fish, Forcing Chains, Multi-Sector Locking.

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 (9)
  1. Step 33 · 2-String Kite advanced
    Rules out 6 from R3C7.
  2. Step 34 · Multi-Sector Locking advanced
    Rules out 7 from R1C7; 4 from R3C5; 8 from R3C5.
  3. Step 35 · Advanced Innies (3+ sectors) advanced
    Rules out 2 from R3C5, R4C5, R4C6; 6 from R3C5; 9 from R3C5.
  4. Step 40 · Coloring/Multi-coloring expert
    Rules out 1 from R4C6.
  5. Step 41 · Advanced Innies (3+ sectors) advanced
    Rules out 6 from R4C5.
  6. Step 43 · Forcing Chains expert
    Rules out 3 from R3C5.
  7. Step 48 · Advanced Innies (3+ sectors) advanced
    Rules out 3 from R4C1; 6 from R4C6.
  8. Step 56 · Advanced Innies (3+ sectors) advanced
    Rules out 2 from R1C5, R2C5; 4 from R2C5; 8 from R2C5.
  9. Step 59 · Finned Fish expert
    Rules out 9 from R2C8, R2C9.

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.