Dosun Fuwari

Rules

Place balloons, i.e. white circles and iron balls, i.e. black circles into some empty cells of the grid so that each thickly outlined region contains one balloon and one iron ball. Balloons are light and float, and thus must be placed at the top of the grid, immediately under black cells, or under other balloons. Iron balls are heavy and sink, and thus must be placed at the bottom of the grid, immediately above a black cell, or above other iron balls.

(Rules and example from WPC 2017 IB)

History of the puzzle

First appeared on Nikoli vol 151 (2015). Dosun and Fuwari are both Japanese onomatopoeia corresponding to iron balls dropping and balloons floating, respectively.

Appearances in the past WPCs

• WPC 2017/Round 13 by Prasanna Seshadri