牛吃草（二分）

题目链接：点击打开链接

代码：

#include<stdio.h>
#include<math.h>
#define pi acos(-1.0)
#define inf 10000000
struct circle
{
    double x,y;
    double r;
} c1,c2;
double  get_juli(double x1,double y1,double x2,double y2)
{
    return sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2));
}
double get_mianji(circle c1,circle c2)
{
    double dis=get_juli(c1.x,c1.y,c2.x,c2.y);
    if(dis>=c1.r+c2.r)
        return 0;
    double min_r=c1.r<c2.r?c1.r:c2.r;
    double max_r=c1.r>c2.r?c1.r:c2.r;
    if(min_r+dis<=max_r)
        return pi*min_r*min_r;
    double  a=acos((c1.r*c1.r+dis*dis-c2.r*c2.r)/2/c1.r/dis);
    double b=acos((c2.r*c2.r+dis*dis-c1.r*c1.r)/2/c2.r/dis);
    double area1=a*c1.r*c1.r;
    double area2=b*c2.r*c2.r;
    double ans=area1+area2;
    double area_que=sin(a)*c1.r*dis;
    ans-=area_que;
    return ans;
}
int main()
{
    int q;
    scanf("%d",&q);
    while(q--)
    {
//        double x0,y0,x1,y1,r;
        scanf("%lf%lf%lf%lf%lf",&c1.x,&c1.y,&c2.x,&c2.y,&c1.r);
        double mianji=pi*c1.r*c1.r/2.0;
        double l=0,r=inf,mid;
        while(r-l>=1e-9)
        {
            mid=(r+l)/2.0;
            c2.r=mid;
            if(get_mianji( c1, c2)>=mianji)
                r=mid;
            else
                l=mid;
        }
        printf("%.4lf\n",r);
    }
}