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Consecutive Sudoku

Bars between cells mark every pair of consecutive digits; where there is no bar, the neighbours are not consecutive.

4 5 8 9 2 3

An example Consecutive puzzle: a bar marks cells that differ by 1 — here 4|5 and 8|9.

Consecutive Sudoku marks the borders between some cells with a short bar. A bar means the two digits either side are consecutive — they differ by exactly 1. In the full version every such pair is marked, so a plain border between two cells is a clue too: it says those digits are not consecutive. Read together, the bars and the gaps solve the grid.

The rule: a bar means "differ by one"

Wherever you see a bar, the two neighbouring digits are a consecutive pair like 4 and 5, or 7 and 8 — in either order. Where there is no bar (in the full version) the neighbours differ by 2 or more. Below, the top two pairs carry bars and the bottom pair does not.

4 5 3 4 6 2

Bars mark consecutive pairs (4-5, 3-4). No bar between 6 and 2 — they differ by more than 1.

Reading a bar

A bar restricts both cells to a consecutive pair: 1-2, 2-3, 3-4, 4-5, 5-6, 6-7, 7-8 or 8-9. Every digit has two consecutive neighbours except the extremes — 1 pairs only with 2, and 9 pairs only with 8. That makes the ends of the range the easiest place to start: a bar touching a 9 forces the neighbour to 8, and a bar touching a 1 forces a 2.

9 8 1 2

A bar on a 9 forces an 8; a bar on a 1 forces a 2 — the extremes have only one consecutive partner.

The negative constraint does the heavy lifting

In a full Consecutive puzzle, the missing bars carry as much information as the printed ones. A blank border beside a 5 rules out both 4 and 6 in the neighbour; a blank border beside a 3 rules out 2 and 4. Every unmarked edge quietly removes two candidates, and on the hardest grids that steady stream of eliminations is what breaks the deadlock — solvers who only use the printed bars grind to a halt.

Solving strategy

  • Start at the extremes. A bar on a 1 or 9 forces its partner immediately.
  • Follow bar chains. A run of bars is a run of steps of ±1 — like a gentle thermometer that can go either way, it constrains a whole line.
  • Mine the blank edges. In the full version, each missing bar removes two candidates from the neighbour — use them relentlessly.
  • Feed the grid. Each forced digit behaves like a given for its row, column and box.

Common mistakes

  • Reading a bar as an order. A bar never says which side is larger — 4-5 and 5-4 both satisfy it.
  • Ignoring the missing bars. In full Consecutive, a blank border is a genuine "not consecutive" clue, not the absence of one.
  • Confusing it with a bar that means a ratio. Consecutive bars mean a difference of 1, not a doubling — that is Kropki's black dot, a different variant.
  • Forgetting ordinary Sudoku. The bars are an extra layer over the usual row, column and box rules.

Can I play it here?

Not yet — Consecutive 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: