EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 1, puzzle 117: 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 117 of 150 in Extreme Killer Sudoku 1
Difficulty
Expert 2 (expert and beyond), from the final, hardest third of the book
Key technique
Coloring/Multi-coloring
Hard steps
8 of 98 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) (×3), Multi-Sector Locking (×2), 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 (8)
  1. Step 22 · Multi-Sector Locking advanced
    Rules out 3 from R2C6.
  2. Step 27 · Advanced Innies (3+ sectors) advanced
    Rules out 9 from R1C5, R4C5; 1 from R5C1, R5C7; 2 from R5C1.
  3. Step 39 · Advanced Innies (3+ sectors) advanced
    Rules out 7 from R5C9.
  4. Step 47 · Empty Rectangle advanced
    Rules out 1 from R7C3.
  5. Step 48 · Multi-Sector Locking advanced
    Rules out 8 from R3C3, R3C4.
  6. Step 49 · Coloring/Multi-coloring expert
    Rules out 2 from R3C4.
  7. Step 54 · Forcing Chains expert
    Rules out 3 from R1C6.
  8. Step 76 · Advanced Innies (3+ sectors) advanced
    Rules out 2 from R4C3; 5 from R4C3; 9 from R4C3.

The book

No starting digits at all: just cages and their totals. Sudoku rules, plus arithmetic, plus a lot of nerve.

150 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.

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Try a free sample puzzle (PDF) · prints on A4 or US Letter

More step-by-step solutions: Extreme Sudoku 1 · Extreme Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.