EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 3, puzzle 34: 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 34 of 150 in Extreme Killer Sudoku 3
Difficulty
Expert 3 (expert and beyond), from the opening third of the book
Key technique
Coloring/Multi-coloring
Hard steps
11 of 81 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) (×4), Empty Rectangle (×2), Finned Fish, Forcing Chains, Multi-Sector Locking, X-Wing/Swordfish.

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 20 · Multi-Sector Locking advanced
    Rules out 9 from R8C7.
  2. Step 21 · Advanced Innies (3+ sectors) advanced
    Places 9 in R2C6 and rules out 9 from R1C4, R1C5, R1C6, R2C1 and 12 more; 2 from R2C5, R3C5; 4 from R2C5, R3C5.
  3. Step 39 · Empty Rectangle advanced
    Rules out 5 from R6C2.
  4. Step 40 · Empty Rectangle advanced
    Rules out 5 from R6C7.
  5. Step 41 · Advanced Innies (3+ sectors) advanced
    Rules out 2 from R1C5, R6C5; 6 from R1C5, R6C5; 7 from R6C1.
  6. Step 48 · Coloring/Multi-coloring expert
    Rules out 9 from R4C2, R5C2.
  7. Step 50 · X-Wing/Swordfish advanced
    Rules out 5 from R1C2, R1C4, R1C7, R5C2 and 2 more.
  8. Step 53 · Forcing Chains expert
    Rules out 7 from R1C4, R6C5, R9C4; 8 from R1C6, R1C8, R1C9, R4C4 and 2 more; 4 from R2C4.
  9. Step 57 · Advanced Innies (3+ sectors) advanced
    Rules out 2 from R6C9; 7 from R6C9.
  10. Step 58 · Finned Fish expert
    Rules out 8 from R6C8, R6C9.
  11. Step 59 · Advanced Innies (3+ sectors) advanced
    Rules out 2 from R6C2.

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

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