Shade some cells so that shaded sections form rectangles, and numbered thickly outlined regions contain the given number of shaded cells, not necessarily consecutive/joined. Blocks without numbers can have any number of shaded cells. Rectangles must not share sides.
(Rules and example from WPC 2017 IB)
History of the puzzle
First appeared on Nikoli volume 122 (2008). Its inventor is unknown. The name Chocona is a result of the contraction of a very long name チョコに国境なし ("no borders for chocolates").
Appearances in the past WPCs
- WPC 2017/Round 7 by Prasanna Seshadri