【HDOJ】5017 Ellipsoid

简单地模拟退火。

 /* 5017 */
 #include <cstdio>
 #include <cstring>
 #include <cstdlib>
 #include <cmath>

 #define INF 1e30

 const double eps = 1e-;
 const double next = 0.99;
 int dir[][] = {
     {-, }, {, }, {, -}, {, },
     {-, }, {-, -}, {, -}, {, }
 };
 double a, b, c, d, e, f;

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

 double getZ(double x, double y) {
     double A, B, C, delta, tmp;
     double z1, z2;

     A = c;
     B = d*y + e*x;
     C = a*x*x + b*y*y + f*x*y - 1.0;
     tmp = B*B - *A*C;
     if (tmp < )
         return INF;
     delta = sqrt(tmp);
     z1 = (-B+delta)/(2.0*A);
     z2 = (-B-delta)/(2.0*A);

     return fabs(z1) < fabs(z2) ? z1:z2;
 }

 int main() {
     double x, y, z;
     double xx, yy, zz;
     double step, tmp, ans;
     int i;

     #ifndef ONLINE_JUDGE
         freopen("data.in", "r", stdin);
         freopen("data.out", "w", stdout);
     #endif

     while (scanf("%lf%lf%lf%lf%lf%lf",&a,&b,&c,&d,&e,&f) != EOF) {
         x = ;
         y = ;
         z = getZ(x, y);
         ans = Length(x, y, z);
         step = .;
         while (step > eps) {
             for (i=; i<; ++i) {
                 xx = x + dir[i][]*step;
                 yy = y + dir[i][]*step;
                 zz = getZ(xx, yy);
                 if (zz >= INF)
                     continue;
                 tmp = Length(xx, yy, zz);
                 if (tmp < ans) {
                     x = xx;
                     y = yy;
                     z = zz;
                     ans = tmp;
                 }
             }
             step *= next;
         }
         printf("%.7lf\n", ans);
     }

     return ;
 }