438 - The Circumference of the Circle【几何】

单纯的是为存模板 QAQ

#include<cstdio>#include<cmath>#include<cstring>#include<iostream>#include<algorithm>using namespace std;struct Point{    double x,y;    Point(double x = 0,double y = 0):x(x),y(y){};};//两点的距离double DistancePoint(Point a,Point b){    double x = a.x - b.x;    double y = a.y - b.y;    return sqrt(x * x + y * y);}typedef Point Vector;//-----------------------------------------------------------------------Vector operator +(Vector A,Vector B){return Vector(A.x + B.x,A.y + B.y);}Vector operator -(Vector A,Vector B){return Vector(A.x - B.x,A.y - B.y);}Vector operator *(Vector A,double p){return Vector(A.x * p,A.y * p);}Vector operator /(Vector A,double p){return Vector(A.x / p,A.y / p);}bool operator < (const Point &a,const Point &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; else return 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;}//----------------------------------------------------------------------------//点乘积   计算角度double Dot(Vector A,Vector B){return A.x * B.x + A.y * B.y;}double Length(Vector A){return sqrt(Dot(A,A));}double Angle(Vector A,Vector B){    return acos(Dot(A,B) / Length(A) / Length(B));}//----------------------------------------------------------------------------//叉积    面积的2倍double Cross(Vector A,Vector B){return A.x * B.y - A.y * B.x;}double Area2(Point A,Point B,Point C){    return Cross(B - A,C - A);}//向量旋转Vector Rotate(Vector A,double rad){    return Vector(A.x * cos(rad) - A.y * sin(rad),A.x * sin(rad) + A.y * cos(rad));}//求法线Vector Normal(Vector A){    double L = Length(A);    return Vector(- A.y / L, A.x / L);}//--------------------------------------------------------------------------------//求交点Point GetLineIntersection(Point P,Vector v,Point Q,Vector w){    Vector u = P - Q;    double t = Cross(w,u) / Cross(v,w);    return P + v * t;}//点到直线 P到A Bdouble DistanceToLine(Point P,Point A,Point B){    Vector v1 = B - A,v2 = P - A;    return fabs(Cross(v1,v2)) / Length(v1);}//点到线段double DistanceToSegment(Point P,Point A,Point B){    if(A == B) return Length(P - A);    Vector v1 = B - A,v2 = P - A, v3 = P - B;    if(dcmp(Dot(v1,v2)) < 0) return Length(v2);    else if(dcmp(Dot(v1,v3)) > 0) return Length(v3);    else  return fabs(Cross(v1,v2)) / Length(v1);}//点在直线上的投影Point GetLineProjection(Point P,Point A,Point B){    Vector v = B - A;    return A + v * (Dot(v,P - A) / Dot(v,v));}//相交判定bool SegmentProperIntersection(Point a1,Point a2,Point b1,Point b2){    double c1 = Cross(a2 - a1,b1 - a1), c2 = Cross(a2 - a1,b2 - a1);    double c3 = Cross(b2 - b1,a1 - b1), c4 = Cross(b2 - b1,a2 - b1);    return dcmp(c1) * dcmp(c2) < 0 && dcmp(c3) * dcmp(c4) < 0;}//允许在端点相交bool OnSegment(Point p,Point a1,Point a2){    return dcmp(Cross(a1 - p,a2 - p)) == 0 && dcmp(Dot(a1 - p,a2 - p)) < 0;}//------------------------------------------------------------------------------double x[3],y[3];double pi = acos(-1.0);//求垂直向量Vector Solve(Vector v){    return Vector(-v.y,v.x);}int main(){    while(scanf("%lf%lf",&x[0],&y[0]) != EOF){        scanf("%lf%lf%lf%lf",&x[1],&y[1],&x[2],&y[2]);        double x1 = (x[0] + x[1]) / 2;        double y1 = (y[0] + y[1]) / 2;        double x2 = (x[0] + x[2]) / 2;        double y2 = (y[0] + y[2]) / 2;        Vector v1 = Vector(x[0] - x[1],y[0] - y[1]);        Vector v2 = Vector(x[0] - x[2],y[0] - y[2]);        Vector v3 = Solve(v1);        Vector v4 = Solve(v2);        //printf("%f %f %f %f\n",x1,y1,x2,y2);        //printf("%f %f %f %f\n",v3.x,v3.y,v4.x,v4.y);        Point z = GetLineIntersection(Point(x1,y1),v3,Point(x2,y2),v4);        //printf("%f %f\n",z.x,z.y);        double r = DistancePoint(z,Point(x[0],y[0]));        //printf("%f\n",r);        double d = pi * r * 2;        printf("%.2f\n",d);    }    return 0;}