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

 1 #include <iostream>

 2 #include<cstdio>

 3 #include<cmath>

 4 #include<cstring>

 5 using namespace std;

 6 #define eps 1e-8

 7 const double PI=acos(-1.0);

 8 double l,d,s;

 9 double solve(){

10 

11     if(s-d<eps)//1 

12         return PI*s*s;

13     double dist=sqrt(0.25*l*l+d*d),ans=0;

14     if(s-dist<eps){//2

15         double angle=acos(d/s);

16         ans=(PI-angle)*s*s+s*d*sin(angle);

17     

18     }else{//3,4

19         double angle=asin(0.5*l/dist);

20         ans+=(PI-angle)*s*s+0.5*l*d;

21         s-=dist;

22         angle+=0.5*PI;

23         ans+=angle*s*s;

24         if(s+s-l>eps){

25             double angle1=acos(0.5*l/s);

26             ans-=angle1*s*s-0.5*sin(angle1)*s*l;

27         }

28         

29     }

30     return ans;

31 }

32 int main(int argc, char** argv) {

33     int t;

34     double ans;

35     scanf("%d",&t);

36     while(t--){

37         scanf("%lf%lf%lf",&l,&d,&s);

38         ans=solve();

39         printf("%.2lf\n",ans);

40     }

41     return 0;

42 }