HDU 1724 辛普森积分公式

code：

#include <iostream>#include <cmath>#include <iomanip>using namespace std;typedef double ld;const ld eps = 1e-10;ld a, b, l, r;ld getf(ld x){return b / a * sqrt(a * a - x * x);}ld cal(ld l, ld r){    ld mid = (l + r) / 2;    return (r - l) * (getf(l) + 4 * getf(mid) + getf(r)) / 6;}ld simpson(ld l, ld r){    ld mid = (l + r)/ 2;    ld sa = cal(l, r);    ld la = cal(l, mid), ra = cal(mid, r);    if(fabs(sa - la - ra) <= eps) return sa;    return simpson(l, mid) + simpson(mid, r);}int main(){    int t;    cin >> t;    while(t--){        cin >> a >> b >> l >> r;        cout <<fixed << setprecision(3) << 2 * simpson(l, r) << endl;    }    return 0;}