Author: Sashika
Draw few rectangular loops through the centers of unshaded cell so that every unshaded cell is used. The sides of different rectangles may intersect each other, but not overlap. Two rectangles must have a common vertex in the marked cells and all cells where two rectangles share a vertex are marked.
Grid control: To draw a line press the mouse button at a start cell and move mouse to another cell holding the button. You cam click on marked cells to note position of recatngles touching in this point. More details about grid control are at the help page.