HDU 5017 Ellipsoid（西安网络赛K题）

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HDU 5017 Ellipsoid

题目链接

思路：模拟退火大法好！

代码:

#include <cstdio>#include <cstring>#include <cmath>#include <algorithm>using namespace std;const int D[8][2] = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}, {1, 1}, {-1, -1}, {1, -1}, {-1, 1}};double a, b, c, d, e, f;const double INF = 1e9;const double eps = 1e-8;double dis(double x, double y, double z) {return sqrt(x * x + y * y + z * z);}double cal(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;double del = B * B - 4 * A * C;if (del < 0) return 1e10;del = sqrt(del);double z1 = (-B + del) / A / 2;double z2 = (-B - del) / A / 2;if (dis(x, y, z1) < dis(x, y, z2)) return z1;return z2;}double solve() {double x = 0, y = 0, z = sqrt(1.0 / c);double step = 1.0, r = 0.99;while (step > eps) {for (int i = 0; i < 8; i++) {double xx = x + step * D[i][0];double yy = y + step * D[i][1];double zz = cal(xx, yy);if (zz > INF) continue;if (dis(xx, yy, zz) < dis(x, y, z)) {x = xx; y = yy; z = zz;}}step *= r;}return dis(x, y, z);}int main() {while (~scanf("%lf%lf%lf%lf%lf%lf", &a, &b, &c, &d, &e, &f)) {printf("%.7lf\n", solve());}return 0;}

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