EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 3, puzzle 89: 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 89 of 150 in Extreme Killer Sudoku 3
Difficulty
Expert 3 (expert and beyond), from the middle third of the book
Key technique
Coloring/Multi-coloring
Hard steps
11 of 94 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) (×2), Empty Rectangle (×2), Multi-Sector Locking (×2), Sue de Coq (×2), 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 (11)
  1. Step 17 · Empty Rectangle advanced
    Rules out 9 from R3C5.
  2. Step 18 · Multi-Sector Locking advanced
    Rules out 3 from R1C6, R2C6, R5C6, R6C6 and 4 more.
  3. Step 24 · Empty Rectangle advanced
    Rules out 3 from R4C8.
  4. Step 25 · Advanced Innies (3+ sectors) advanced
    Rules out 1 from R1C6, R7C6; 2 from R1C6, R7C6; 4 from R1C6, R7C6.
  5. Step 33 · Coloring/Multi-coloring expert
    Rules out 9 from R6C1, R7C2.
  6. Step 37 · Multi-Sector Locking advanced
    Rules out 9 from R4C3.
  7. Step 38 · Finned Fish expert
    Rules out 3 from R4C1, R4C2.
  8. Step 39 · Forcing Chains expert
    Rules out 6 from R1C6.
  9. Step 71 · Sue de Coq advanced
    Rules out 5 from R4C1, R5C1; 8 from R4C1, R5C1.
  10. Step 73 · Sue de Coq advanced
    Rules out 1 from R4C2, R5C2; 4 from R4C2, R5C2, R6C2; 2 from R9C3.
  11. Step 74 · Advanced Innies (3+ sectors) advanced
    Rules out 1 from R3C5; 9 from R4C5, R5C5.

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.