HDU 1969 Pie

二分答案+验证（这题精度卡的比较死）

#include<stdio.h>

#include<math.h>

#define eps 1e-7

const int ff = 11111;

double a[ff];

double pi = acos(-1.0);

int main()

{

    int sb;

    scanf("%d", &sb);

    while (sb--)

    {

        int m, n;

        scanf("%d%d", &m, &n);

        int i, j;

        double maxn = 0;

        for (i = 1; i <= m; i++)

        {

            scanf("%lf", &a[i]);

            a[i] = a[i] * a[i] * pi;

            if (a[i] > maxn) maxn = a[i];

        }

        double minn = 0;

        double midn = (minn + maxn) / 2.0;

        while (1)

        {

            if (maxn - minn < eps)

            {

                printf("%.4lf\n", midn);

                break;

            }

            else

            {

                int sum = 0, flag;

                for (i = 1; i <= m; i++) sum += (int)((1.0*a[i] / midn));

                if (sum >= n+1) flag = 1;

                else flag = 0;

                if (flag) minn = midn, midn = (minn + maxn) / 2.0;

                else maxn = midn, midn = (minn + maxn) / 2.0;

            }

        }

    }

    return 0;

}