UVALive 3635 Pie（二分法）

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<string>
#include<cmath>
#include<map>
#include<set>
#include<vector>
#include<algorithm>
#include<stack>
#include<queue>
#include<cctype>
#include<sstream>
using namespace std;
#define pii pair<int,int>
#define LL long long int
const double eps=1e-10;
const int INF=1000000000;
const int maxn=10000+10;
const double pi=acos(-1);
int N,F,T;
double r[maxn],maxr,s[maxn];
bool ok(double x)
{
    int f=0;
    for(int i=0;i<N;i++)
    {
        f+=(int)(s[i]/x);
        if(f>=F) return true;
    }
    return false;
}
int main()
{
    //freopen("in1.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d%d",&N,&F);
        maxr=-1;
        F++;
        for(int i=0; i<N; i++)
        {
            scanf("%lf",&r[i]);
            maxr=max(r[i],maxr);
            s[i]=r[i]*r[i]*pi;
        }

        double L=0,R=maxr*maxr*pi;
        for(int i=0;i<1000;i++)
        {
            double m=(L+R)/2;
            if(ok(m)) L=m;
            else R=m;
        }
        printf("%.4lf\n",R);
    }
    //fclose(stdin);
    //fclose(stdout);
    return 0;
}