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#define _sign(x) ((x)>eps?1:((x)<-eps?2:0))
struct point{double x,y;};
double xmult(point p1,point p2,point p0){
return (p1.x-p0.x)*(p2.y-p0.y)-(p2.x-p0.x)*(p1.y-p0.y);
}
//判定凸多边形,顶点按顺时针或逆时针给出,允许相邻边共线
int is_convex(int n,point* p){
int i,s[3]={1,1,1};
for (i=0;i<n&&s[1]|s[2];i++)
s[_sign(xmult(p[(i+1)%n],p[(i+2)%n],p[i]))]=0;
return s[1]|s[2];
}
//判定凸多边形,顶点按顺时针或逆时针给出,不允许相邻边共线
int is_convex_v2(int n,point* p){
int i,s[3]={1,1,1};
for (i=0;i<n&&s[0]&&s[1]|s[2];i++)
s[_sign(xmult(p[(i+1)%n],p[(i+2)%n],p[i]))]=0;
return s[0]&&s[1]|s[2];
}
//判定凸多边形,顶点按顺时针或逆时针给出,允许相邻边共线
int is_convex(int n,point* p){
int i,s[3]={1,1,1};
for (i=0;i<n&&s[1]|s[2];i++)
s[_sign(xmult(p[(i+1)%n],p[(i+2)%n],p[i]))]=0;
return s[1]|s[2];
}
//判定凸多边形,顶点按顺时针或逆时针给出,不允许相邻边共线
int is_convex_v2(int n,point* p){
int i,s[3]={1,1,1};
for (i=0;i<n&&s[0]&&s[1]|s[2];i++)
s[_sign(xmult(p[(i+1)%n],p[(i+2)%n],p[i]))]=0;
return s[0]&&s[1]|s[2];
}