EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 2, puzzle 72: 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 72 of 150 in Extreme Killer Sudoku 2
Difficulty
Expert 2 (expert and beyond), from the middle third of the book
Key technique
Finned Fish
Hard steps
8 of 90 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), Multi-Sector Locking (×2), Forcing Chains, 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 (8)
  1. Step 13 · Multi-Sector Locking advanced
    Rules out 3 from R1C1, R1C3, R2C3, R3C3 and 2 more.
  2. Step 16 · Advanced Innies (3+ sectors) advanced
    Rules out 7 from R1C6, R8C4; 9 from R1C6, R5C6, R8C4; 2 from R5C6.
  3. Step 20 · Advanced Innies (3+ sectors) advanced
    Rules out 6 from R3C5, R4C5, R5C5; 9 from R4C5, R4C6, R5C5; 2 from R6C5.
  4. Step 54 · XY-Wing advanced
    Rules out 5 from R1C3.
  5. Step 55 · Multi-Sector Locking advanced
    Rules out 7 from R3C2.
  6. Step 57 · Finned Fish expert
    Rules out 2 from R2C1.
  7. Step 58 · Finned Fish expert
    Rules out 4 from R2C1.
  8. Step 79 · Forcing Chains expert
    Rules out 1 from R1C3.

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.

Buy on Amazon US Buy on Amazon UK
Other Amazon stores
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 Sudoku 3 · Extreme Killer Sudoku 3.