【HDOJ】2289 Cup

二分。另外，圆台体积为v = PI*(r*r+r*R+R*R)*H/3。注意精度。

 #include <cstdio>
 #include <cmath>

 #define exp 1e-9

 const double PI = acos(-1.0);

 int main() {
     int t;
     double r, R, H, v, lf, rt, mid, r0, nv;
     scanf("%d", &t);

     while (t--) {
         scanf("%lf%lf%lf%lf", &r, &R, &H, &v);
         lf = ;
         rt = H;
         while (rt >= lf+exp) {
             mid = (lf+rt)/;
             r0 = mid*(R-r)/H+r;
             nv = PI*(r*r+r*r0+r0*r0)*mid/;
             if (fabs(nv -v) <= exp)
                 break;
             if (nv < v)
                 lf = mid;
             else
                 rt = mid;
         }
         printf("%.6lf\n", mid);
     }

     return ;
 }