BZOJ3564 信号增幅仪

http://www.lydsy.com/JudgeOnline/problem.php?id=3564

思路:先旋转坐标系，再缩进x坐标，把椭圆变成圆，然后做最小圆覆盖。

还有，为什么用srand()又错了啊。。。

#include<cstdio>

#include<cstring>

#include<cmath>

#include<algorithm>

#include<iostream>

const double Pi=acos(-);

const double eps=1e-;

struct Point{

    double x,y;

    Point(){}

    Point(double x0,double y0):x(x0),y(y0){}

}p[];

int n;

struct Line{

    Point s,e;

    Line(){}

    Line(Point s0,Point e0):s(s0),e(e0){}

};

int read(){

    int t=,f=;char ch=getchar();

    while (ch<''||ch>''){if (ch=='-') f=-;ch=getchar();}

    while (''<=ch&&ch<=''){t=t*+ch-'';ch=getchar();}

    return t*f;

}

Point operator +(Point p1,Point p2){

    return Point(p1.x+p2.x,p1.y+p2.y);

}

Point operator -(Point p1,Point p2){

    return Point(p1.x-p2.x,p1.y-p2.y);

}

double operator *(Point p1,Point p2){

    return p1.x*p2.y-p1.y*p2.x;

}

Point operator /(Point p1,double x){

    return Point(p1.x/x,p1.y/x);

}

Point operator *(Point p,double x){

    return Point(p.x*x,p.y*x);

}

double sqr(double x){return x*x;}

double dis(Point p){

    return sqrt(sqr(p.x)+sqr(p.y));

}

double dis(Point p1,Point p2){

    return dis(p1-p2);

}

Point turn(Point p,double ang){

    double Cos=cos(ang);

    double Sin=sin(ang);

    double x=p.x*Cos-p.y*Sin;

    double y=p.x*Sin+p.y*Cos;

    return Point(x,y);

}

Point inter(Line p1,Line p2){

    double k1=(p2.e-p1.s)*(p1.e-p1.s);

    double k2=(p1.e-p1.s)*(p2.s-p1.s);

    double t=(k2)/(k1+k2);

    double x=p2.s.x+(p2.e.x-p2.s.x)*t;

    double y=p2.s.y+(p2.e.y-p2.s.y)*t;

    return Point(x,y);

}

Point solve(Point p1,Point p2,Point p3){

    Point a=(p1+p2)/2.0;

    Point b=(p2+p3)/2.0;

    return inter(Line(a,a+turn(p2-a,Pi/2.0)),Line(b,b+turn(p3-b,Pi/2.0)));

}

int main(){

    //srand(233);

    n=read();

    for (int i=;i<=n;i++)

        p[i].x=read(),p[i].y=read();

    double ang=read();ang/=180.0;ang*=Pi;

    double len=read();

    for (int i=;i<=n;i++)

       p[i]=turn(p[i],-ang);

    for (int i=;i<=n;i++)

       p[i].x/=len;

    for (int i=;i<=n;i++)

        std::swap(p[rand()%n+],p[rand()%n+]);

    Point O=p[];double r=;

    for (int i=;i<=n;i++)

      if (dis(p[i],O)+eps>r){

        O=p[i];r=0.0;

        for (int j=;j<i;j++)

            if (dis(p[j],O)+eps>r){

               O=(p[i]+p[j])/2.0;

               r=dis(O,p[j]);

               for (int k=;k<j;k++)

                  if (dis(p[k],O)+eps>r){

                    O=solve(p[i],p[j],p[k]);

                    r=dis(O,p[k]);

                  }

            }

      }

    printf("%.3lf\n",r);

}