hdu2289二分答案 圆台体积

精度小一点就能过

#include<bits/stdc++.h>
#define maxn 1000000009
#define esp 1e-9
#define PI 3.1415926535897932384626

using namespace std;

double r,R,H,V,V1,h1,R1;

double func(double h1){
    R1=r+(h1/H)*(R-r);
    V1=((double)1/3)*PI*h1*(R1*R1+r*r+R1*r);
    return V1;
}

int main(){
    int t;
    scanf("%d",&t);
    while(t--){
        scanf("%lf%lf%lf%lf",&r,&R,&H,&V);
        double ll=0,rr=H;
        while(abs(rr-ll)>esp){
            h1=(ll+rr)/2;
            if(func(h1)<V)
                ll=h1;
            else rr=h1;
        }
        printf("%.6lf
",(ll+rr)/2);
    }
}