EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 2, puzzle 24: 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 24 of 150 in Extreme Killer Sudoku 2
Difficulty
Expert 3 (expert and beyond), from the opening third of the book
Key technique
Coloring/Multi-coloring
Hard steps
9 of 87 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 (×3), Advanced Innies (3+ sectors) (×2), Forcing Chains, Remote Pairs.

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 11 · Multi-Sector Locking advanced
    Rules out 9 from R3C4, R3C6, R4C4, R5C4 and 1 more; 4 from R6C4, R9C6; 5 from R6C4, R9C6.
  2. Step 14 · Advanced Innies (3+ sectors) advanced
    Rules out 4 from R3C6; 5 from R3C6, R4C4, R5C4; 6 from R4C4, R5C4.
  3. Step 39 · Multi-Sector Locking advanced
    Rules out 4 from R1C7, R1C8; 5 from R7C8; 6 from R7C8.
  4. Step 40 · Coloring/Multi-coloring expert
    Rules out 2 from R3C7.
  5. Step 41 · Coloring/Multi-coloring expert
    Rules out 4 from R2C7, R3C7.
  6. Step 42 · Forcing Chains expert
    Rules out 8 from R3C5.
  7. Step 53 · Multi-Sector Locking advanced
    Rules out 5 from R2C3.
  8. Step 55 · Advanced Innies (3+ sectors) advanced
    Rules out 1 from R4C2.
  9. Step 56 · Remote Pairs expert
    Rules out 7 from R1C4; 8 from R1C4.

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.