EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 3, puzzle 82: 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 82 of 150 in Extreme Killer Sudoku 3
Difficulty
Expert 2 (expert and beyond), from the middle third of the book
Key technique
Coloring/Multi-coloring
Hard steps
7 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: 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: Multi-Sector Locking (×2), Advanced Innies (3+ sectors), Empty Rectangle, 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 (7)
  1. Step 19 · Multi-Sector Locking advanced
    Rules out 9 from R2C3; 8 from R4C8, R4C9, R5C9, R6C9.
  2. Step 21 · Advanced Innies (3+ sectors) advanced
    Rules out 1 from R5C2; 6 from R5C2; 7 from R5C2, R5C6.
  3. Step 27 · Forcing Chains expert
    Rules out 1 from R1C1, R1C5, R1C9, R2C1 and 20 more; 7 from R1C1, R2C1, R3C1, R4C1 and 13 more; 9 from R1C4, R2C4, R2C9, R3C4 and 6 more.
  4. Step 44 · Multi-Sector Locking advanced
    Rules out 7 from R2C3.
  5. Step 46 · Coloring/Multi-coloring expert
    Rules out 5 from R2C3.
  6. Step 56 · Empty Rectangle advanced
    Rules out 6 from R9C8.
  7. Step 58 · Coloring/Multi-coloring expert
    Rules out 6 from R2C5.

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.