9×9 · Constraint

Dutch Whispers Sudoku

Along a Dutch whisper line, neighbouring digits must differ by at least 4.

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An example Dutch Whispers puzzle: neighbours on the orange line differ by at least 4 — here 1, 5, 9, 4.

Dutch Whispers Sudoku draws lines along which neighbouring digits must differ by at least 4. It is the gentler cousin of German Whispers (which demands a gap of 5): the smaller gap means the digits still zig-zag between low and high, but with a little more freedom — and, crucially, the 5 is allowed back onto the line.

The rule: a gap of four or more

Walk the line one step at a time; each adjacent pair must be at least 4 apart. A 1 can sit next to 5, 6, 7, 8 or 9; a 2 next to 6, 7, 8 or 9. The line below reads 1-6-2-7-3, and every neighbouring gap clears 4.

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Every neighbour differs by 4 or more: 1-6-2-7-3.

A worked example, step by step

Take a line where one cell is a 5 — the digit German Whispers forbids, but Dutch allows.

5

Step 0. A 5 sits on the line.

Step 1 — the neighbours must be 4 away. A cell next to the 5 has to differ from it by at least 4, so it must be 1 or lower, or 9 or higher. On a 1–9 grid that leaves only 1 or 9.

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Step 1. Both neighbours of the 5 must be 1 or 9.

Step 2 — the pattern spreads. Whichever of 1 or 9 lands next to the 5, its own neighbour must then be 4 away from it, and so on. Each placement forces the next, and the line snakes between low and high all the way along.

The pairs that fit

Running through them: a 1 pairs with 5, 6, 7, 8 or 9; a 2 with 6–9; a 3 with 7, 8 or 9; a 4 with 8 or 9; and a 5 only with 1 or 9. The extremes are the sharpest clues — a 4 or a 5 on the line has very few legal neighbours, so start there.

Solving strategy

  • Chase the tight digits. A 4 (only 8 or 9) or a 5 (only 1 or 9) forces its neighbours hard.
  • Colour low and high. The line alternates between lower and higher digits — mark the swing.
  • Remember 5 is allowed. Unlike German Whispers, a 5 can sit on a Dutch line (its neighbours are 1 or 9).
  • Feed the grid. Each digit fixed on the line behaves like a given for its row, column and box.

Common mistakes

  • Banning the 5. That is the German Whispers rule (gap 5); Dutch (gap 4) permits a 5, paired with 1 or 9.
  • Using a gap of 5. Dutch needs only a difference of 4 — don't over-tighten it.
  • Two close digits in a row. Adjacent cells must clear the gap of 4; the line can never step, say, 4 to 6.
  • Forgetting ordinary Sudoku. Line cells still can't repeat within a row, column or box.

Can I play it here?

Not yet — Dutch Whispers Sudoku isn't one of the puzzle types SudokuStreak generates for now. But you can learn its rules above, and there's plenty here to sink your teeth into meanwhile: