Author: Andrey Bogdanov
Draw a single continuous loop in the grid using horizontal and vertical line segments so that the loop visits every square exactly once. Each cell belongs to one of two types: those where line goes straight and those where line turns. Dots are located between all horizontally neighboring cells of the same type.
Grid control: To draw a line press the mouse button at a start cell and move mouse to another cell holding the button. More details about grid control are at the help page.