All Sudoku Variants
9×9 · Constraint

Renban Sudoku

Also known as Renban Groups

Marked lines must contain a set of consecutive digits, in any order — a run like 4-5-6-7 scrambled along the line.

2 96475

An example Renban puzzle: the pink line holds a run of consecutive digits in any order — here {4, 5, 6, 7}.

Renban Sudoku draws coloured lines across the grid, and each line — a "renban group" — must hold a set of consecutive digits, in any order. A four-cell renban might read 5-3-6-4 along the line, but the digits form the unbroken run 3-4-5-6. There are no repeats and no gaps: it is a straight of consecutive numbers, simply scrambled.

The rule: a scrambled run of consecutive digits

Take the cells a renban line covers, ignore their order, and they must form a run like 3-4-5-6 or 6-7-8-9 with nothing missing and nothing repeated. In the example below the line reads 5, 3, 6, 4 — out of order, but together exactly the run 3 to 6. Every row, column and box still follows the normal Sudoku rules on top of this.

5364

Scrambled along the line (5, 3, 6, 4), the digits form the consecutive run 3-4-5-6.

Think in ranges, not sequences

The order on the line never matters — only the set of values does. That means a renban is really a statement about range: an n-cell renban holds n different consecutive digits, so its highest and lowest values are exactly n − 1 apart. A four-cell renban spans 3, so it must be one of the runs 1-4, 2-5, 3-6, 4-7, 5-8 or 6-9 — and it can never contain both a 1 and a 9, whose gap of 8 is far too wide.

One digit pins the whole run

Because the run is contiguous, a single known digit dramatically narrows it. If a four-cell renban contains a 6, the run must include 6, so it is 3-6, 4-7, 5-8 or 6-9. Every one of those excludes 1 and 2, so those digits vanish from all four cells at once — a large elimination from a single clue.

6no 1,2no 1,2no 1,2

A four-cell renban holding a 6 must be one of the runs 3-6, 4-7, 5-8 or 6-9 — so 1 and 2 leave every cell on the line.

Solving strategy

  • Turn each line into a range. Note its length, then list the handful of runs it could be before looking at anything else.
  • Anchor on a given digit. One number on a renban collapses the list of possible runs and usually strikes the extreme digits from every cell.
  • Use the units. If a renban lies inside one row or box, its digits cannot repeat anyway — but even crossing units, the consecutive-set rule holds.
  • Watch the ends of the number line. Long renbans are pushed toward the middle (a 6-cell line can only be 1-6, 2-7, 3-8 or 4-9), so 1 and 9 are rare on them.

Common mistakes

  • Reading the order as the answer. The digits along the line are scrambled; only the set of values matters.
  • Allowing a gap. A renban is consecutive — 3-4-6 is not a valid three-cell renban, because 5 is missing.
  • Allowing a repeat. The run uses each of its consecutive digits once; no value appears twice on the line.
  • Forgetting the span limit. An n-cell renban spans exactly n − 1, which alone rules out the widest digit pairs.

Can I play it here?

Not yet — Renban 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: