EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 3, puzzle 77: 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 77 of 150 in Extreme Killer Sudoku 3
Difficulty
Expert 3 (expert and beyond), from the middle third of the book
Key technique
Finned Fish
Hard steps
9 of 83 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) (×2), 2-String Kite, Coloring/Multi-coloring, Empty Rectangle, Forcing Chains, Multi-Sector Locking, XY-Wing.

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 (9)
  1. Step 40 · Advanced Innies (3+ sectors) advanced
    Rules out 1 from R4C2.
  2. Step 41 · Finned Fish expert
    Rules out 6 from R3C4.
  3. Step 42 · Forcing Chains expert
    Rules out 9 from R1C2.
  4. Step 58 · Empty Rectangle advanced
    Rules out 4 from R7C1.
  5. Step 59 · Multi-Sector Locking advanced
    Rules out 2 from R8C3.
  6. Step 60 · Advanced Innies (3+ sectors) advanced
    Rules out 8 from R1C5; 5 from R4C2, R9C5; 7 from R4C2.
  7. Step 68 · XY-Wing advanced
    Rules out 7 from R4C4.
  8. Step 71 · 2-String Kite advanced
    Rules out 7 from R7C4.
  9. Step 72 · Coloring/Multi-coloring expert
    Rules out 2 from R4C2, R6C4, R8C5.

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.