【HDOJ】1969 Pie

二分。

#include <stdio.h>
#include <math.h>

const double eps = 1e-6;
double areas[10001];

int main() {
    int case_n, n, f, m;
    double r, sum, l, mid, PI;
    int i;

    PI = acos(-1);

    scanf("%d", &case_n);

    while (case_n--) {
        scanf("%d %d", &n, &f);
        sum = 0.0f;
        for (i=0; i<n; ++i) {
            scanf("%lf", &r);
            areas[i] = PI*r*r;
            sum += areas[i];
        }
        l = 0.0f;
        ++f;
        r = sum/f;
        while (r-l > eps) {
            mid = (l+r)/2;
            m = 0;
            for (i=0; i<n; ++i)
                m += (int)(areas[i]/mid);
            if (m < f)
                r = mid;
            else
                l = mid;
        }
        printf("%.4lf
", l);
    }

    return 0;
}