poj3737

三分法求单峰函数极值

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#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
using namespace std;

#define pi acos(double(-1))
#define eps 10E-11

double s;

int dblcmp(double &a, double &b)
{
    if (a - eps > b)
        return 1;
    if (a + eps < b)
        return -1;
    return 0;
}

double cal(double &r)
{
    double R = s / pi / r - r;
    double h = sqrt(R * R - r * r);
    return r * r * pi * h / 3;
}

int main()
{
    //freopen("t.txt", "r", stdin);
    while (scanf("%lf", &s) != EOF)
    {
        double l = 0;
        double r = sqrt(s / pi);
        while (dblcmp(l, r) < 0)
        {
            double r1 = l + (r - l) / 3;
            double r2 = r - (r - l) / 3;
            double vol1 = cal(r1);
            double vol2 = cal(r2);
            if (dblcmp(vol1, vol2) < 0)
                l = r1;
            else
                r = r2;
        }
        double R = s / pi / r - r;
        double h = sqrt(R * R - r * r);
        double vol = r * r * pi * h / 3;
        printf("%.2f\n%.2f\n%.2f\n", vol, h, r);
    }
    return 0;
}