Jigsaw Sudoku: follow the region boundary

Nine-cell regions replace the boxes

A 9×9 Jigsaw keeps ordinary rows and columns. Its nine outlined regions each contain nine cells and must each contain 1–9 once. Their shapes need not be 3×3 squares, so the remembered Classic box boundaries cannot supply eliminations.

Nikoli — Sudoku rules · Grandmaster Puzzles — Jigsaw rules

Our region, written as coordinates

Consider region R containing A1, A2, A3, B1, B2, B3, C1, C2 and D1: nine connected cells. Suppose its first eight listed cells contain 1–8 in order, with D1 the only gap. Region R then forces D1=9.

This is one partial teaching region, not a complete tiling of a playable board. C3 is nearby but outside R. Do not silently include it because a familiar Classic top-left box would contain it.

Nearby does not define a shared region

Adjacent cells across a boundary may still see each other through their row or column. Distant cells may see each other through the same irregular region. When using a pair or a locked candidate, name the shared unit instead of relying on how close the cells look.

A way to keep your place

Choose one region and count its nine cells before listing missing digits. Coordinates can help when the outline turns several corners. Inspecting one complete region is easier to audit than glancing at many incomplete regions. This is our suggested reading routine, not a requirement to finish one region before touching another.

Sudoku-Y currently offers Classic and Killer. This variation is not yet a playable mode here. Always read the puzzle maker’s rules before applying a technique.

Try before looking

References and further reading

Read the source explanations and compare them with our examples. Links are references, not endorsements or claims of affiliation.

• Nikoli — Sudoku rules
• Grandmaster Puzzles — Jigsaw rules