简单地模拟退火。
1 /* 5017 */ 2 #include <cstdio> 3 #include <cstring> 4 #include <cstdlib> 5 #include <cmath> 6 7 #define INF 1e30 8 9 const double eps = 1e-8; 10 const double next = 0.99; 11 int dir[8][2] = { 12 {-1, 0}, {1, 0}, {0, -1}, {0, 1}, 13 {-1, 1}, {-1, -1}, {1, -1}, {1, 1} 14 }; 15 double a, b, c, d, e, f; 16 17 double Length(double x, double y, double z) { 18 return sqrt(x*x + y*y + z*z); 19 } 20 21 double getZ(double x, double y) { 22 double A, B, C, delta, tmp; 23 double z1, z2; 24 25 A = c; 26 B = d*y + e*x; 27 C = a*x*x + b*y*y + f*x*y - 1.0; 28 tmp = B*B - 4*A*C; 29 if (tmp < 0) 30 return INF; 31 delta = sqrt(tmp); 32 z1 = (-B+delta)/(2.0*A); 33 z2 = (-B-delta)/(2.0*A); 34 35 return fabs(z1) < fabs(z2) ? z1:z2; 36 } 37 38 int main() { 39 double x, y, z; 40 double xx, yy, zz; 41 double step, tmp, ans; 42 int i; 43 44 #ifndef ONLINE_JUDGE 45 freopen("data.in", "r", stdin); 46 freopen("data.out", "w", stdout); 47 #endif 48 49 while (scanf("%lf%lf%lf%lf%lf%lf",&a,&b,&c,&d,&e,&f) != EOF) { 50 x = 0; 51 y = 0; 52 z = getZ(x, y); 53 ans = Length(x, y, z); 54 step = 1.; 55 while (step > eps) { 56 for (i=0; i<8; ++i) { 57 xx = x + dir[i][0]*step; 58 yy = y + dir[i][1]*step; 59 zz = getZ(xx, yy); 60 if (zz >= INF) 61 continue; 62 tmp = Length(xx, yy, zz); 63 if (tmp < ans) { 64 x = xx; 65 y = yy; 66 z = zz; 67 ans = tmp; 68 } 69 } 70 step *= next; 71 } 72 printf("%.7lf ", ans); 73 } 74 75 return 0; 76 }