EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 3, puzzle 90: 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 90 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
9 of 86 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: Multi-Sector Locking (×4), Advanced Innies (3+ sectors), Forcing Chains, XYZ-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 34 · XYZ-Wing advanced
    Rules out 3 from R2C1.
  2. Step 43 · Multi-Sector Locking advanced
    Rules out 9 from R5C8, R6C8.
  3. Step 44 · Forcing Chains expert
    Rules out 1 from R4C3; 2 from R4C3; 5 from R4C3.
  4. Step 45 · Multi-Sector Locking advanced
    Rules out 9 from R8C4.
  5. Step 62 · Multi-Sector Locking advanced
    Rules out 5 from R4C6.
  6. Step 63 · Advanced Innies (3+ sectors) advanced
    Rules out 3 from R4C2; 4 from R4C2; 8 from R4C2.
  7. Step 68 · Multi-Sector Locking advanced
    Rules out 7 from R5C5, R5C6.
  8. Step 69 · Finned Fish expert
    Rules out 3 from R5C6, R6C6.
  9. Step 70 · Finned Fish expert
    Rules out 4 from R5C6, R6C6.

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.