Dosun-Fuwari

Dosun-Fuwari is a logic puzzle published by Nikoli. The task consists of a grid divided into regions. The grid may contain black cells; black cells do not belong to any region. The aim is to place one black circle and one white circle in each region according to the following rules:

• White circles ("balloons") are light and float, so they must be placed either into the top cell of the grid or into the cell right under the black cell or under other white circle.
• Black circles ("iron balls") are heavy and sink, so they must be placed either into the bottom cell of the grid or into the cell right over the black cell or over other black circle.

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