EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 1, puzzle 140: 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 140 of 150 in Extreme Killer Sudoku 1
Difficulty
Expert 3 (expert and beyond), from the final, hardest third of the book
Key technique
Finned Fish
Hard steps
11 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) (×3), 2-String Kite (×2), Forcing Chains, Multi-Sector Locking, Remote Pairs, Sue de Coq.

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 14 · Multi-Sector Locking advanced
    Rules out 7 from R3C1, R3C2, R3C3, R3C9; 8 from R3C1, R3C2, R3C3, R3C4 and 1 more; 9 from R3C1, R3C9.
  2. Step 15 · Advanced Innies (3+ sectors) advanced
    Rules out 3 from R5C2; 5 from R5C2, R6C7, R7C7; 7 from R6C2, R6C7, R7C7.
  3. Step 17 · Forcing Chains expert
    Rules out 6 from R4C5.
  4. Step 37 · Advanced Innies (3+ sectors) advanced
    Rules out 4 from R4C1, R4C2, R4C3, R5C1; 3 from R5C1; 7 from R5C2.
  5. Step 58 · 2-String Kite advanced
    Rules out 4 from R3C9.
  6. Step 59 · Advanced Innies (3+ sectors) advanced
    Rules out 3 from R2C4.
  7. Step 60 · Finned Fish expert
    Rules out 4 from R8C3.
  8. Step 67 · 2-String Kite advanced
    Rules out 8 from R2C9.
  9. Step 69 · Remote Pairs expert
    Rules out 1 from R4C2; 2 from R4C2.
  10. Step 70 · Sue de Coq advanced
    Rules out 1 from R8C1; 2 from R9C1.
  11. Step 71 · Finned Fish expert
    Rules out 4 from R5C5.

The book

No starting digits at all: just cages and their totals. Sudoku rules, plus arithmetic, plus a lot of nerve.

150 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 Sudoku 2 · Extreme Killer Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.