soj 1698 Hungry Cow_三角函数

题目链接

题意：有只牛要吃草，现在有个墙挡着，给你绑着牛的绳的长度，墙的长度，绳原点到墙的距离，问牛能在多大的面积里吃草

思路：分为四种情况，详情请看书。被dp卡着这题没做成

 #include <iostream>
 #include<cstdio>
 #include<cmath>
 #include<cstring>
 using namespace std;
 #define eps 1e-8
 const double PI=acos(-1.0);
 double l,d,s;
 double solve(){

     if(s-d<eps)//1
         return PI*s*s;
     double dist=sqrt(0.25*l*l+d*d),ans=;
     if(s-dist<eps){//
         double angle=acos(d/s);
         ans=(PI-angle)*s*s+s*d*sin(angle);

     }else{//3,4
         double angle=asin(0.5*l/dist);
         ans+=(PI-angle)*s*s+0.5*l*d;
         s-=dist;
         angle+=0.5*PI;
         ans+=angle*s*s;
         if(s+s-l>eps){
             double angle1=acos(0.5*l/s);
             ans-=angle1*s*s-0.5*sin(angle1)*s*l;
         }

     }
     return ans;
 }
 int main(int argc, char** argv) {
     int t;
     double ans;
     scanf("%d",&t);
     while(t--){
         scanf("%lf%lf%lf",&l,&d,&s);
         ans=solve();
         printf("%.2lf\n",ans);
     }
     return ;
 }