EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 3, puzzle 112: 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 112 of 150 in Extreme Killer Sudoku 3
Difficulty
Expert 3 (expert and beyond), from the final, hardest third of the book
Key technique
Remote Pairs
Hard steps
9 of 58 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: Remote Pairs

A chain of cells that all hold the same pair alternates between the two digits. Cells that see both ends of an odd-length link cannot hold either digit.

Other advanced and expert techniques in this solve: Advanced Innies (3+ sectors) (×2), Multi-Sector Locking (×2), 2-String Kite, Coloring/Multi-coloring, Forcing Chains, X-Wing/Swordfish.

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 11 · Multi-Sector Locking advanced
    Rules out 9 from R2C5, R3C5, R4C5, R5C5 and 1 more.
  2. Step 13 · Advanced Innies (3+ sectors) advanced
    Places 7 in R5C1, 8 in R7C7 and rules out 7 from R2C1, R2C2, R3C1, R3C2 and 14 more; 8 from R2C5, R3C5, R4C5, R5C5 and 9 more; 4 from R2C6, R3C6, R4C6.
  3. Step 29 · X-Wing/Swordfish advanced
    Rules out 8 from R3C2, R3C4, R4C2, R4C4.
  4. Step 32 · 2-String Kite advanced
    Rules out 9 from R6C3.
  5. Step 33 · Multi-Sector Locking advanced
    Rules out 1 from R2C2; 4 from R4C4; 9 from R7C3.
  6. Step 35 · Advanced Innies (3+ sectors) advanced
    Rules out 1 from R7C1.
  7. Step 37 · Remote Pairs expert
    Rules out 5 from R7C3.
  8. Step 40 · Coloring/Multi-coloring expert
    Rules out 8 from R2C2, R3C6, R4C1, R5C4.
  9. Step 54 · Forcing Chains expert
    Rules out 2 from R2C7.

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.