hdu 1969 Pie 二分

/*
 * hdu1969.c
 *
 *  Created on: 2011-10-9
 *      Author: bjfuwangzhu
 */

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#define nmax 10010
#define pi acos(-1.0)
#define eps 1.0e-5
double volume[nmax];
int cmp(int n, double aver) {
    int i, temp;
    for (i = 0, temp = 0; i < n; i++) {
        temp += (int) (volume[i] / aver);
    }
    return temp;
}
void solve(int n, int f, double sum) {
    double left, right, mid;
    left = 0.0, right = sum / f;
    while (fabs(left - right) > eps) {
        mid = (left + right) / 2;
        if (cmp(n, mid) >= f) {
            left = mid;
        } else {
            right = mid;
        }
    }
    printf("%.4lf\n", mid);
}
int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif
    int t, n, f, i, r;
    double sum;
    scanf("%d", &t);
    while (t--) {
        scanf("%d %d", &n, &f);
        for (i = 0, sum = 0.0; i < n; i++) {
            scanf("%d", &r);
            volume[i] = pi * r * r;
            sum += volume[i];
        }
        solve(n, f + 1, sum);
    }
    return 0;
}