EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 2, puzzle 141: 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 141 of 150 in Extreme Killer Sudoku 2
Difficulty
Expert 3 (expert and beyond), from the final, hardest third of the book
Key technique
Forcing Chains
Hard steps
11 of 99 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: Forcing Chains

Try each candidate of one cell in turn. Every choice leads to the same result, so that result must be true.

Other advanced and expert techniques in this solve: Empty Rectangle (×4), Advanced Innies (3+ sectors) (×2), Multi-Sector Locking (×2), Coloring/Multi-coloring, Finned Fish.

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 14 · Multi-Sector Locking advanced
    Rules out 1 from R2C3, R9C3; 7 from R4C6, R5C6, R9C6; 6 from R9C7, R9C8.
  2. Step 17 · Advanced Innies (3+ sectors) advanced
    Rules out 8 from R1C4, R2C4, R9C4; 9 from R1C4, R2C4, R9C4; 7 from R2C4, R9C4.
  3. Step 24 · Advanced Innies (3+ sectors) advanced
    Rules out 1 from R9C4; 4 from R9C4.
  4. Step 25 · Forcing Chains expert
    Rules out 4 from R1C4.
  5. Step 45 · Empty Rectangle advanced
    Rules out 1 from R6C7.
  6. Step 47 · Empty Rectangle advanced
    Rules out 4 from R2C9.
  7. Step 49 · Multi-Sector Locking advanced
    Rules out 8 from R7C1, R7C2, R7C8, R7C9.
  8. Step 50 · Empty Rectangle advanced
    Rules out 8 from R3C7.
  9. Step 81 · Empty Rectangle advanced
    Rules out 6 from R5C6.
  10. Step 83 · Coloring/Multi-coloring expert
    Rules out 4 from R8C1.
  11. Step 84 · Finned Fish expert
    Rules out 5 from R5C6.

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.

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