is a logic puzzle. The goal is to blacken some cells of the grid. All the black cells form one contiguous region. No 2 x 2 cell area within the grid can contain all black cells. Clue cells with numbers may not be filled in and tell the length of each consecutive black cell block in the eight surrounding cells. If there's more than one digit in a cell, the groups of black cells have to be separated by at least one white cell. Question marks can be used instead of clue numbers. Each question mark can represent any nonzero integer.