Flip color with one stroke. Two types of one stroke color puzzle. They are interesting and simple. But not easy. A.Divided The rectangle board have some disordered black and white blocks. The surrounded grey blocks is the transition area. The board is divided into some subregion. Just draw a stroke on the blocks of each subregion. The black and white of the blocks where the line passed are reversed. For the subregion, the color of each row should be the same. The end of the line is next to the