All Sudoku Variants
9×9 · Constraint

Next to Nine Sudoku

The digits printed outside a row or column are exactly the digits directly adjacent to the 9 in that line, listed in increasing order.

8 9 1 1 9 5 1 9 8 5 2 3 61 81 51 8

An example Next to Nine puzzle. Beside row 1, "1 8" are the two digits touching the 9 — the 8 and the 1 either side of it.

Next to Nine Sudoku writes small clue digits outside some rows and columns. Those digits are exactly the ones that sit directly next to the 9 in that line — its immediate neighbours. It is an unusual clue: instead of telling you about the near edge, it pins down the neighbourhood of a single roving digit, the 9.

The rule: the clues border the 9

Find the 9 in a clued row or column. The digits printed outside are precisely the ones touching it — two neighbours normally, or just one if the 9 sits at the very end. The clues are listed in increasing order, not the order they appear beside the 9. Below, the clue "3 8" means a 3 and an 8 flank the 9.

3 8 3 9 8

The clue "3 8" names the two digits touching the 9 — here the 3 to its left and the 8 to its right.

What the clue tells you

Two digits means the 9 has a neighbour on each side, so it cannot be at either end of the line — and neither of those two digits is the 9's far-side neighbour anywhere else. One digit means the 9 is at an end of the row or column, with a single neighbour: a strong placement hint, because only two cells (the two ends) can hold a 9 with just one neighbour.

Solving strategy

  • Count the clue digits. One digit forces the 9 to an end of the line; two digits keep it off both ends.
  • Pair the neighbours. The two clue digits must sit in cells either side of the 9, so wherever the 9 lands, those digits flank it.
  • Cross-reference the 9s. Each row and column has exactly one 9; use the clues together with normal scanning to corner it.
  • Ignore the order. Because clues are sorted, "3 8" tells you the set {3, 8}, not which side each is on — let the rest of the grid decide.

Common mistakes

  • Reading the clue as a position. It lists the 9's neighbours, not cells counted from the edge.
  • Assuming left-to-right order. The clues are in increasing order; the actual sides are set by other constraints.
  • Forgetting the one-digit case. A single clue digit is a powerful signal that the 9 is at an end.
  • Dropping ordinary Sudoku. Rows, columns and boxes still each need 1–9 once.

Can I play it here?

Not yet — Next to Nine 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: