Heyawake is a Nikoli puzzle genre.
- Shade some cells on the grid.
- No two shaded cells may be directly adjacent.
- All unshaded cells must be connected.
- If a region has a number in it, the number of shaded cells in the region must be that number.
- Unshaded cells must not stretch along an orthogonal line crossing two or more borders.
- In some rulesets, it is stated explicitly that all regions are rectangles; sometimes, the generalization in which regions may take arbitrary shapes is called “Heyawacky”. (Notably, in the rectangular case, the rule involving two borders can be described instead as “containing three or more regions”, which is no longer true when the regions are not convex.)