EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 2, puzzle 103: 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 103 of 150 in Extreme Killer Sudoku 2
Difficulty
Expert 2 (expert and beyond), from the final, hardest third of the book
Key technique
Forcing Chains
Hard steps
8 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: Forcing Chains

Try each candidate of one cell in turn. Every choice leads to the same result, so that result must be true.

Other advanced and expert techniques in this solve: Advanced Innies (3+ sectors) (×2), Multi-Sector Locking (×2), 2-String Kite, Coloring/Multi-coloring, 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 (8)
  1. Step 13 · Advanced Innies (3+ sectors) advanced
    Places 7 in R4C6 and rules out 7 from R1C6, R2C6, R3C5, R3C6 and 14 more; 4 from R5C4; 5 from R5C4.
  2. Step 24 · Advanced Innies (3+ sectors) advanced
    Rules out 3 from R3C5, R4C4, R4C5; 2 from R5C4; 9 from R5C7.
  3. Step 61 · Multi-Sector Locking advanced
    Rules out 5 from R6C2.
  4. Step 63 · Forcing Chains expert
    Rules out 5 from R1C5.
  5. Step 66 · Coloring/Multi-coloring expert
    Rules out 1 from R4C2.
  6. Step 67 · XYZ-Wing advanced
    Rules out 2 from R3C2.
  7. Step 68 · 2-String Kite advanced
    Rules out 1 from R7C9.
  8. Step 69 · Multi-Sector Locking advanced
    Rules out 1 from R7C1, R8C1.

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.

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More step-by-step solutions: Extreme Sudoku 1 · Extreme Killer Sudoku 1 · Extreme Sudoku 2 · Extreme Sudoku 3 · Extreme Killer Sudoku 3.