Shakashaka
Logic puzzle
From Wikipedia, the free encyclopedia
Shakashaka (シャカシャカ) is a logic puzzle developed by publisher Nikoli.[1]
An example Shakashaka puzzle
The same puzzle with solution marked in teal
Rules
Shakashaka is played on a rectangular grid of white and black squares. Some black cells may contain a number.
The objective of the puzzle is to place triangles in some of the white cells. There are four kinds of triangles which can be put in squares: 
In the resulting grid,
- The white parts of the grid (uncovered by black triangles) must form a rectangle or a square, not sharing an edge with other white squares/rectangles.
- Black cells with a number must be orthogonally adjacent to the specified number of black triangles.[2]
Computational complexity
It is NP-complete to decide whether a given Shakashaka puzzle has a solution.[3] Furthermore, counting the number of solutions to a given Shakashaka puzzle is #P-complete.[3]
