HDU 5017 Ellipsoid 模拟退火

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>

using namespace std;
const double eps = 1e-8;
const double r = 0.99;	//降温速度
const int dx[] = { 0, 0, 1, -1, 1, -1, 1, -1 };
const int dy[] = { 1, -1, 0, 0, -1, 1, 1, -1 };
double a, b, c, d, e, f;

double dis(double x, double y, double z) {
	return sqrt(x * x + y * y + z * z);
}

//已知x,y,求z
double getz(double x, double y) {
	double A = c, B = e * x + d * y,
		C = a * x * x + b * y * y + f * x * y - 1;
	double delta = B * B - 4 * A * C;
	if (delta < 0) return 1e60;
	double z1 = (-B + sqrt(delta)) / 2 / A,
		z2 = (-B - sqrt(delta)) / 2 / A;
	if (z1 * z1 < z2 * z2) return z1;
	else return z2;
}

double solve() {
	//模拟退火
	double step = 1;	//步长
	double x = 0, y = 0, z;
	while (step > eps) {
		z = getz(x, y);
		for (int i = 0; i < 8; i++) {
			double nx = x + dx[i] * step,
				ny = y + dy[i] * step,
				nz = getz(nx, ny);
			if (nz > 1e30) continue;
			if (dis(nx, ny, nz) < dis(x, y, z)) {
				x = nx; y = ny; z = nz;
			}
		}
		step *= r;
	}
	return dis(x, y, z);
}

int main() {
	while (scanf("%lf%lf%lf%lf%lf%lf", &a, &b, &c, &d, &e, &f) != EOF) {
		printf("%.8f\n", solve());
	}
	return 0;
}