Akari (also known as Light Up) is a well known logic puzzle. The object is to place “lightbulbs” in some grid squares. Each lightbulb illuminates every square in each of the four compass directions (imagine a rook in chess) up until a black cell is hit. Every grid square must be illuminated, but no two lightbulbs may illuminate each other. A black cell with a number indicates how many of the four surrounding cells have a light bulb. The solution is unique.