左眼皮跳跳

A n * m grid as follow: Count the number of triangles, three of whose vertice must be grid-points.Note that the three vertice of the triangle must not be in a line(the right picture is not a

Alice lives in the country where people like to make friends. The friendship is bidirectional and if any two person have no less thank friends in common, they will become friends in several days. Cu