Tatamibari

Tatamibari is a logic puzzle created and published by the Japanese puzzle company Nikoli. Its name comes from the Japanese word for tatami mats, the traditional woven floor mats whose rectangular shapes the puzzle's regions evoke. A tatamibari puzzle presents a rectangular grid containing scattered plus, minus and vertical bar symbols. The solver must partition the whole grid into rectangular regions so that every region contains exactly one symbol, with the shape of each region matching its symbol: a plus symbol must sit inside a square region, a vertical bar must sit inside a region taller than it is wide, and a minus symbol must sit inside a region wider than it is tall. An additional rule forbids four separate regions from meeting at a single corner point, which forces the partition into specific configurations and gives the puzzle its logical structure. Researchers established in a 2020 academic paper that determining whether a tatamibari puzzle has a solution is NP-complete, placing it among the computationally hardest pencil puzzles studied.