zstu 4243 牛吃草(浮点数二分)

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浮点数二分while条件为l<r

#include<iostream>#include<cstdio>#include<cstring>#include<algorithm>#include<cmath>using namespace std;const double eps=1e-6;const double PI=acos(-1.0);struct Circle{    double x,y;    double r;};double calArea(Circle c1, Circle c2){    double d;    double s,s1,s2,s3,angle1,angle2;        d=sqrt((c1.x-c2.x)*(c1.x-c2.x)+(c1.y-c2.y)*(c1.y-c2.y));    if(d>=(c1.r+c2.r))//两圆相离        return 0;    if((c1.r-c2.r)>=d)//两圆内含,c1大        return PI*c2.r*c2.r;    if((c2.r-c1.r)>=d)//两圆内含,c2大        return PI*c1.r*c1.r;    angle1=acos((c1.r*c1.r+d*d-c2.r*c2.r)/(2*c1.r*d));    angle2=acos((c2.r*c2.r+d*d-c1.r*c1.r)/(2*c2.r*d));    s1=angle1*c1.r*c1.r;s2=angle2*c2.r*c2.r;    s3=c1.r*d*sin(angle1);    s=s1+s2-s3;    return s;}bool isZero(double x){    return x>-eps&&x<eps;}int main(){    double x1,y1,x2,y2,r;    int t;    scanf("%d",&t);    while(t--)    {        scanf("%lf%lf%lf%lf%lf",&x1,&y1,&x2,&y2,&r);        Circle c1=Circle{x1,y1,r};        double ans=(PI*r*r)/2;        double d=sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));        double L=0.0,R=d+r;        double rr=0;        while(L<R)        {            double mid=(L+R)/2;            double area=calArea(c1,Circle{x2,y2,mid});            if(isZero(area-ans)) {rr=mid;break;}            else if(ans>area+eps) L=mid;            else R=mid;        }        printf("%.4f\n",rr);    }    return 0;}

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