EXTREMEPUZZLE BOOKS

Extreme Killer Sudoku 1, puzzle 93: 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 93 of 150 in Extreme Killer Sudoku 1
Difficulty
Expert 2 (expert and beyond), from the middle third of the book
Key technique
Remote Pairs
Hard steps
6 of 81 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), 2-String Kite, Forcing Chains, Multi-Sector Locking.

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 (6)
  1. Step 13 · Advanced Innies (3+ sectors) advanced
    Places 6 in R4C2 and rules out 6 from R1C2, R2C2, R3C2, R4C1 and 13 more; 4 from R4C5; 7 from R4C5.
  2. Step 44 · Advanced Innies (3+ sectors) advanced
    Rules out 7 from R5C5, R6C5; 9 from R5C5, R6C5.
  3. Step 51 · Multi-Sector Locking advanced
    Rules out 1 from R2C2, R2C3; 3 from R2C4.
  4. Step 54 · Remote Pairs expert
    Rules out 2 from R3C1, R3C2; 6 from R3C1.
  5. Step 62 · 2-String Kite advanced
    Rules out 7 from R7C2.
  6. Step 63 · Forcing Chains expert
    Rules out 5 from R1C1, R1C2, R1C3, R1C6 and 7 more; 7 from R1C1, R1C2, R2C6, R8C2; 8 from R1C1, R1C2, R1C3, R2C6 and 5 more.

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.

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