hdu 1742 Ellipse

（自适应辛普森模板）

#include"bits/stdc++.h"using namespace std;int a,b,l,r;double f(double x){    return 2.0*b/a*sqrt(a*a-x*x);}double simpson(double l, double r){    return (r-l)/6*(f(l) + 4*f((l+r)/2) + f(r));}double solve(double l, double r, double eps){    double mid = (l+r)/2;    double now = simpson(l,r), L = simpson(l,mid), R = simpson(mid,r);    if(fabs(L+R-now) < 15*eps) return L+R+(L+R-now)/15.0;    else return solve(l,mid,eps/2) + solve(mid,r,eps/2);}int main(){    int T;    scanf("%d",&T);    while(T--){        scanf("%d%d%d%d",&a,&b,&l,&r);        printf("%.3lf\n",solve(l,r,1e-6));    }    return 0;}