German Whispers Sudoku Explained in One Short Example
A four-cell green line starts with 2 and 7, which are 5 apart. 7 then 4 fails because they are only 3 apart, and 2, 7, 1, 8 swings low, high, low, high.
Transcript
The rule
A German whispers line is a green line through the grid. Any two cells next to each other on the line must differ by at least 5. Digits can repeat on the line when sudoku rules allow it.
The rule splits the digits into low (1 to 4) and high (6 to 9), and 5 is left out entirely. Once you know whether one cell is low or high, the whole line falls into a pattern.
Worth memorizing
5 can never go on a green line.
No digit from 1 to 9 is 5 away from 5. Every solver learns this first.
4 can only sit next to 9, and 6 only next to 1.
Digits swing low (1–4) and high (6–9) along the line, so every other cell has the same type.
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