uva 12097

题目: http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=42065

#include <cstdio>
#include <cmath>
using namespace std;

const double PI = acos(-1);
double v[10005];
int N, F;

bool test(double x)
{
    int tot = 0;
    for(int i=0; i<N; i++) {
        tot += floor(v[i] / x);
    }
    return tot >= F;
}

int main ()
{
    int T, r;
    scanf("%d", &T);
    while(T--) {
        scanf("%d%d", &N, &F);
        ++F;
        double lb = 0, ub = -1;
        for(int i=0; i<N; i++) {
            scanf("%d", &r);
            v[i] = PI * r * r;
            if(v[i] > ub)    ub = v[i];
        }

        ub += 1;
        while(lb + 1e-5< ub) { // [, )
            double mid = (lb + ub) / 2;
            if(test(mid))    lb = mid;
            else ub = mid;
        }
        printf("%.4lf\n", lb);
    }
    return 0;
}