POJ3122-Pie-二分答案

#include <cstdio>
#include <algorithm>
#include <cstring>

using namespace std;

const double esp = 1e-6;
const double PI = 3.14159265359;

int T,N,F,radii[10010];

int main()
{
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d%d",&N,&F);
        F++;
        double low = 0,high=0,mid;

        for(int i=0;i<N;i++)
        {
            scanf("%d",&radii[i]);
            high = max(high,radii[i]*radii[i]*PI);
        }

        while(high-low>esp)
        {
            int piece = 0;
            mid = (low+high)/2;
            for(int i=0;i<N;i++)
            {
                double v = radii[i]*radii[i]*PI;
                int cnt = 0;
                while((cnt+1)*mid < v) cnt++;
                piece += cnt;
            }

            //printf("low=%f high=%f piece=%d\n",low,high,piece);
            if(piece >= F) low = mid;
            else high = mid;
        }
        printf("%.4f\n",mid);
    }
}