hdu 3264 09 宁波 现场 E - Open-air shopping malls 计算几何 二分

#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cstring>
#include <cmath>
#include <algorithm>
#define eps 1e-10
#define PI acos(-1.0)
using namespace std;
struct point
{
    double x,y;
};
struct circle
{
    point c;
    double r;
}ci[50];
double dis(point p1,point p2)
{
    return sqrt((p1.x-p2.x)*(p1.x-p2.x)+(p1.y-p2.y)*(p1.y-p2.y));
}
double area(point p,double R,circle a)
{

    double d=dis(p,a.c),pp;
    double sa=0,ang1,ang2;
    ang1=acos((a.r*a.r+d*d-R*R)/(2*a.r*d));
    ang2=acos((R*R+d*d-a.r*a.r)/(2*R*d));
    pp=R*sin(ang2);
    sa=ang1*a.r*a.r+ang2*R*R-pp*d;
    return sa;
}
double qsearch(point p,circle a)
{
    double d=dis(p,a.c);
    double l=d,r=sqrt(d*d+a.r*a.r),mid;
    double ans=PI*a.r*a.r/2;
    while(l+eps<r)
    {
        mid=(l+r)/2;
        if(fabs(area(p,mid,a)-ans)<eps)
            return mid;
        else if(ans<area(p,mid,a))
            r=mid;
        else
            l=mid;
    }
    return l;
}
int main()
{
    int t,n;
    point p;
    circle a;
    p.x=2,p.y=0;
    a.c.x=0,a.c.y=0,a.r=1;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        for(int i=0;i<n;i++)
            scanf("%lf%lf%lf",&ci[i].c.x,&ci[i].c.y,&ci[i].r);
        double minn;
        for(int i=0;i<n;i++)
        {
            double maxn=ci[i].r/sqrt(2.0);
            for(int j=0;j<n;j++)
            {
                if(i==j) continue;
                maxn=max(maxn,qsearch(ci[i].c,ci[j]));
            }
            if(i==0)
                minn=maxn;
            else
                minn=min(minn,maxn);
        }
        printf("%.4f\n",minn);
    }
    return 0;
}