HDU1724 Ellipse

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Math is important!! Many students failed in 2+2’s mathematical test, so let's AC this problem to mourn for our lost youth..
Look this sample picture:

A ellipses in the plane and center in point O. the L,R lines will be vertical through the X-axis. The problem is calculating the blue intersection area. But calculating the intersection area is dull, so I have turn to you, a talent of programmer. Your task is tell me the result of calculations.(defined PI=3.14159265 , The area of an ellipse A=PI*a*b )

InputInput may contain multiple test cases. The first line is a positive integer N, denoting the number of test cases below. One case One line. The line will consist of a pair of integers a and b, denoting the ellipse equation , A pair of integers l and r, mean the L is (l, 0) and R is (r, 0). (-a <= l <= r <= a).OutputFor each case, output one line containing a float, the area of the intersection, accurate to three decimals after the decimal point.Sample Input

Sample Output

6.283

3.142

几何

simpson积分强行搞

 #include<iostream>

 #include<cstdio>

 #include<algorithm>

 #include<cstring>

 #include<cmath>

 using namespace std;

 const double eps=1e-;

 const int mxn=;

 int read(){

     int x=,f=;char ch=getchar();

     while(ch<'' || ch>''){if(ch=='-')f=-;ch=getchar();}

     while(ch>='' && ch<=''){x=x*-''+ch;ch=getchar();}

     return x*f;

 }

 int a,b;

 inline double f(double x){

     return b*sqrt((double)-(x*x/(double)a/a));

 }

 inline double sim(double l,double r){

     return (r-l)/*(f(l)+*f((l+r)/)+f(r));

 }

 double solve(double l,double r){

     double mid=(l+r)/;

     double res=sim(l,r);

 //    printf("l:%.3f  r:%.3f  res:%.3f\n",l,r,res);

     if(fabs(sim(l,mid)+sim(mid,r)-res)<=eps)return res;

     return solve(l,mid)+solve(mid,r);

 }

 int main(){

     int T=read();

     double l,r;

     while(T--){

         a=read();b=read();

         l=read();r=read();

         double ans=solve(l,r);

         printf("%.3f\n",*ans);

     }

     return ;

 }