POJ3122

題目鏈接：http://poj.org/problem?id=3122

用二分法找到最大的餡餅的面積

代碼：

<span style="font-size:18px;">#include<cstdio>
#include<iostream>
using namespace std;
const int maxn = 10010;
double r[maxn];
const double pi=3.14159265359;

const double esp=1e-6;
int main()
{
    int t;
    scanf("%d", &t);
    while(t--)
    {
        int n, f;
        scanf("%d%d", &n, &f);
        f++;
        double maxt = -1;
        for(int i = 1; i<= n; i++)
        {
            scanf("%lf", &r[i]);
            r[i] *= r[i];
            if(r[i]>maxt)
            {
                maxt = r[i];
            }
        }
        double low = 0;
        double mid = 0;
        while(maxt - low > esp)
        {
            mid = (low + maxt) / 2;
            int cnt = 0;
            for(int i = 1; i<= n; i++)
            {
                cnt += (int)r[i] / mid;
            }
            if(cnt < f)
            {
                maxt = mid;
            }
            else
            {
                low = mid;
            }
        }
        printf("%.4f\n", mid*pi);
    }
    return 0;
}</span>