Shakashaka

Shakashaka is a logic puzzle developed by the Japanese puzzle publisher Nikoli, the company also responsible for popularizing sudoku. A Shakashaka puzzle is played on a rectangular grid of white and black cells; some of the black cells carry a number. The solver must place black triangles inside white cells so that every remaining white area forms a rectangle or a square, while each numbered black cell touches exactly that many black triangles among its neighboring cells. As with other Nikoli puzzles, a valid Shakashaka grid has exactly one solution, and working toward it requires the solver to satisfy the triangle-placement and the numeric adjacency constraints at the same time, which typically rules out easy trial and error once several triangles have been placed. The puzzle takes its name from a Japanese onomatopoeia and belongs to the same family of pencil logic puzzles as sudoku, nurikabe, and slitherlink, sharing their single-grid, single-solution format and appearing in the same puzzle magazines and collections that Nikoli publishes.