ACM学习历程——HDU5017 Ellipsoid（模拟退火）（2014西安网赛K题）

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cmath>
#define esp 1e-7

using namespace std;

bool flag;
double a, b, c, d, e, f;

double getz(double x, double y)
{
    double A = c;
    double B = d*y + e*x;
    double C = f*x*y + a*x*x + b*y*y - 1.0;
    double v = B*B - 4*A*C;
    if (v < 0)
    {
        flag = 0;
        return 0;
    }
    flag = 1;
    v = sqrt(v);
    double z1 = (v-B) / A / 2.0;
    double z2 = (-v-B) / A / 2.0;
    if (fabs(z1) < fabs(z2))
        return z1;
    else
        return z2;
}

double dis(double x, double y)
{
    double z = getz(x, y);
    if (flag == 0)
        return 0;
    return sqrt(x*x + y*y + z*z);
}

double qt()//模拟退火
{
    double x = 0, y = 0, Min = dis(x, y);
    double xx, yy, len;
    double step = 1;
    while (step >= esp)
    {
        for (int dx = -1; dx <= 1; ++dx)
        {
            for (int dy = -1; dy <= 1; ++dy)
            {
                if (dx == 0 && dy == 0)
                    continue;
                xx = x + step*dx;
                yy = y + step*dy;
                len = dis(xx, yy);
                if (flag && len < Min)
                {
                    Min = len;
                    x = xx;
                    y = yy;
                }
            }
        }
        step *= 0.97;
    }
    return Min;
}

int main()
{
    //freopen("test.txt", "r", stdin);
    while (scanf("%lf%lf%lf%lf%lf%lf", &a, &b, &c, &d, &e, &f) != EOF)
    {
        printf("%.7lf\n", qt());
    }
    return 0;
}