求两条线段的交点

　　两条线段的两个端点坐标(x1,y1) (x2,y2) (x3,y3) (x4,y4)

　　b1=(y2-y1)*x1+(x1-x2)*y1

　　b2=(y4-y3)*x3+(x3-x4)*y3

　　D=(x2-x1)(y4-y3)-(x4-x3)(y2-y1)

　　D1=b2*(x2-x1)-b1*(x4-x3)

　　D2=b2*(y2-y1)-b1*(y4-y3)

　　交点(x0,y0)

　　x0=D1/D   y0=D2/D

推导：http://www.cnblogs.com/dwdxdy/p/3230485.html

 

E. Covered Points

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

You are given nn segments on a Cartesian plane. Each segment's endpoints have integer coordinates. Segments can intersect with each other. No two segments lie on the same line.

Count the number of distinct points with integer coordinates, which are covered by at least one segment.