HDU 5858 Hard problem（计算几何）【较难】【多校联合8.18】

题目链接：http://acm.split.hdu.edu.cn/showproblem.php?pid=5858

解题思路：

看懂这个图，这个题就能A掉了。
下面是AC代码：

#include<cstdio>#include<cstring>#include<cmath>#include<algorithm>using namespace std;#define PI acos(-1.0)int main(){    int r1,r,t;    scanf("%d",&t);    while(t--)    {scanf("%d",&r1);        r=(double)r1;        double x=1.25/(sqrt(2.0));        double jiaodu=(acos(x))*2.0;        double hudu=acos(x)*2.0;        double area1=1.0*r*r*hudu*0.5;        double area2=0.5*r*r*sin(hudu);        double area=area1-area2;        double hudu2=2.0*PI-2.0*acos(-sqrt(2.0)/4.0);        double area3=0.25*r*r*hudu2/2.0;        area=area3-area-0.25*r*r*sin(hudu2)*0.5;        area*=2.0;        printf("%.2lf\n",area);    }    return 0;}