Moonsun
Draw one loop that visits all suns or all moons in every region and alternates between them.
Controls
Draw one closed loop through cell centres. It crosses each region boundary exactly twice. In every region the loop passes through all symbols of one type, either all white suns or all black moons, and none of the other type. Consecutive regions along the loop must switch type. Empty regions are bridges.
Brain training · PuzGo