二分搜索 HDOJ 2289 Cup

题目传送门

/*
    二分搜索：枚举高度，计算体积与给出的比较。 
*/
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>
using namespace std;

const int MAXN = 1e3 + 10;
const int INF = 0x3f3f3f3f;
const double EPS = 1e-8;
const double PI = acos (-1.0);
double r, R, H, V;
double x;

double cal(double h1)    {
    double u = r + (R - r) * h1 / H;        //上底
    double V1 = PI / 3.0 * h1 * (r * r + r * u + u * u);    //圆台计算公式
    return V1;
}

int main(void)  {       //HDOJ 2289 Cup
    //freopen ("HDOJ_2289.in", "r", stdin);

    int T;  scanf ("%d", &T);
    while (T--) {
        scanf ("%lf%lf%lf%lf", &r, &R, &H, &V);
        double mid;
        double low = 0, upp = H;
        while (upp - low > EPS)  {
            mid = (low + upp) / 2;
            if (cal (mid) - V > EPS)    upp = mid;
            else low = mid;
        }
        printf ("%.6f
", mid);
    }

    return 0;
}