Heyablock

Heyablock ("Heyawake-Block") is a logic puzzle invented by Atsumi Hirose (Japan). A rectangular or square grid is divided into regions. The aim is to blacken some cells of a grid according to the following rules:

• All black cells in a region must be connected.
• A cell with a number indicates how many cells in the region must be blackened.
• In regions without a number any amount of cells may be blackened (at least one).
• When two cells are orthogonally adjacent across a region boundary, at least one cell must be white.
• All white cells form one orthogonally connected area.
• A line of connected white cells cannot go through two or more region borders.

Cross+A can solve puzzles from 3 x 3 to 30 x 30.