<span style="font-size:18px;">点到直线距离，，直线相交交点，线段相交，向量点乘，向量叉乘，三角形有向面积，点到直线距离。</span>struct point{double x,y;point(double x=0,double y=0):x(x),y(y) { }};typedef point V;struct circle{point c;double r;circle(point c,double r):c(c),r(r){}point Point(double a){return point(c.x+cos(a)*r,+c.y+sin(a)*r);}};struct line{point c;V v;};V operator + (V a,V b){ return V(a.x+b.x,a.y+b.y);}V operator – (V a,V b){ return V(a.x-b.x,a.y-b.y);}V operator * (V a,double p){return V(a.x*p,a.y*p);}V operator / (V a,double p){return V(a.x/p,a.y/p);}bool operator < (const V& a,const V& b){return a.x<b.x||(a.x==b.x&&a.y<b.y);}const double eps = 1e-10;int dcmp(double x){if(fabs(x)<eps) return 0;elsereturn x<0?-1:1;}bool operator == (const point& a,const point& b){return dcmp(a.x-b.x)==0&&dcmp(a.y-b.y)==0;}double dot(V a,V b){return a.x*b.x+a.y*b.y; }double length(V a){return sqrt(dot(a,a));}double angle(V a,V b){return acos(dot(a,b)/length(a)/length(b)); }double cross(V a,V b){return a.x*b.y-a.y*b.x; }double area2(point a,point b,point c){return cross(b-a,c-a); }/*two line change point返回两线交点(保证有唯一交点)*/point twolineispoint(point p,V v,point q,V w){V u=p-q;double t=cross(w,u)/cross(v,w);return p+v*t;}/*线段是否相交*/bool segmentmeet(point a1,point a2,point b1,point b2){double c1=cross(a2-a1,b1-a1),c2=cross(a2-a1,b2-a1),c3=cross(b2-b1,a1-b1),c4=cross(b2-b1,a1-b1);return dcmp(c1)*dcmp(c2)<0&&dcmp(c3)*dcmp(c4)<0;}/*点到直线距离*/point pointtoline(point p,point a,point b){V v1=b-a,v2=p-a;return fabs(cross(v1,v2))/length(v1);}
不能接受失败，也意味太想去成功了，从心理学上解释，
