Extreme Killer Sudoku 2, puzzle 55: 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.
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: 2-String Kite, Advanced Innies (3+ sectors), 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 (5)
- Step 36 · Advanced Innies (3+ sectors) advanced
Rules out 9 from R7C4, R8C4, R9C4. - Step 37 · Coloring/Multi-coloring expert
Rules out 8 from R3C6. - Step 38 · Forcing Chains expert
Rules out 3 from R1C2. - Step 61 · 2-String Kite advanced
Rules out 5 from R4C2. - Step 64 · Remote Pairs expert
Rules out 1 from R3C6, R8C9, R9C4, R9C5 and 1 more; 3 from R3C6, R8C9, R9C4, R9C5 and 1 more.
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.
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.