EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 3, puzzle 57: 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 57 of 150 in Extreme Killer Sudoku 3
Difficulty
Expert 2 (expert and beyond), from the middle third of the book
Key technique
Finned Fish
Hard steps
10 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: Finned Fish

An X-Wing or Swordfish with one extra candidate (the fin). Cells that are in the fish pattern and also see the fin lose the digit.

Other advanced and expert techniques in this solve: Advanced Innies (3+ sectors) (×3), Multi-Sector Locking (×3), 2-String Kite, 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 (10)
  1. Step 14 · Multi-Sector Locking advanced
    Rules out 9 from R2C4, R6C4, R7C4, R8C4 and 1 more; 8 from R4C1, R4C2, R4C3, R4C4 and 2 more.
  2. Step 16 · Advanced Innies (3+ sectors) advanced
    Rules out 3 from R1C7, R5C3; 8 from R4C7, R5C3, R5C4; 9 from R4C7.
  3. Step 38 · 2-String Kite advanced
    Rules out 7 from R1C3.
  4. Step 40 · Multi-Sector Locking advanced
    Rules out 1 from R4C1.
  5. Step 41 · Advanced Innies (3+ sectors) advanced
    Rules out 6 from R6C9; 7 from R6C9.
  6. Step 43 · Multi-Sector Locking advanced
    Rules out 6 from R3C9, R4C9.
  7. Step 45 · Finned Fish expert
    Rules out 1 from R8C7.
  8. Step 46 · Finned Fish expert
    Rules out 8 from R6C8, R6C9.
  9. Step 48 · Advanced Innies (3+ sectors) advanced
    Rules out 7 from R6C7; 9 from R6C7.
  10. Step 77 · Forcing Chains expert
    Rules out 4 from R1C4.

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

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 Killer Sudoku 2 · Extreme Sudoku 3.