先把椭圆长轴转到x轴上，然后把x轴按照比例缩回去，于是就变成了最小圆覆盖问题，上板子。。。就行
1 /************************************************************** 2 Problem: 3564 3 User: rausen 4 Language: C++ 5 Result: Accepted 6 Time:256 ms 7 Memory:2380 kb 8 ****************************************************************/ 9 10 #include <cstdio> 11 #include <cmath> 12 13 using namespace std; 14 typedef double lf; 15 const int N = 5e4 + 5; 16 const lf pi = acos(-1.0); 17 const lf eps = 1e-7; 18 19 inline int read(); 20 21 template <class T> T sqr(T x) { 22 return x * x; 23 } 24 25 struct point { 26 lf x, y; 27 point() {} 28 point(lf _x, lf _y) : x(_x), y(_y) {} 29 30 inline void get() { 31 x = read(), y = read(); 32 } 33 inline void rev(lf a) { 34 static lf tx, ty; 35 tx = x * cos(a) - y * sin(a), ty = x * sin(a) + y * cos(a); 36 x = tx, y = ty; 37 } 38 39 inline point operator + (const point &p) const { 40 return point(x + p.x, y + p.y); 41 } 42 inline point operator - (const point &p) const { 43 return point(x - p.x, y - p.y); 44 } 45 inline point operator / (lf t) const { 46 return point(x / t, y / t); 47 } 48 inline lf operator * (const point &p) const { 49 return x * p.y - y * p.x; 50 } 51 52 friend inline lf dis2(const point &p) { 53 return sqr((lf) p.x) + sqr((lf) p.y); 54 } 55 friend inline point work(const point &a, const point &b, const point &c) { 56 static point p, q, res; 57 static lf d, ab, bc, ac; 58 p = b - a, q = c - a, d = p * q * 2; 59 if (fabs(d) < eps) { 60 ab = dis2(b - a), bc = dis2(c - b), ac = dis2(c - a); 61 if (ab - bc >= eps && ab - ac >= eps) return (a + b) / 2; 62 if (bc - ab >= eps && bc - ac >= eps) return (b + c) / 2; 63 return (a + c) / 2; 64 } 65 return point(dis2(p) * q.y - dis2(q) * p.y, dis2(q) * p.x - dis2(p) * q.x) / d + a; 66 } 67 } p[N], c[N]; 68 69 int n, cnt; 70 lf alpha, P; 71 72 inline lf min_cover() { 73 static int i, j, k; 74 static lf rad2; 75 rad2 = cnt = 0; 76 for (i = 1; i <= n; ++i) if (dis2(p[i] - c[cnt]) > rad2) { 77 c[cnt] = p[i], rad2 = 0.0; 78 for (j = 1; j < i; ++j) if (dis2(p[j] - c[cnt]) > rad2) { 79 c[cnt] = (p[i] + p[j]) / 2.0, rad2 = dis2(p[i] - c[cnt]); 80 for (k = 1; k < j; ++k) if (dis2(p[k] - c[cnt]) > rad2) 81 c[cnt] = work(p[i], p[j], p[k]), rad2 = dis2(p[i] - c[cnt]); 82 } 83 } 84 return sqrt(rad2); 85 } 86 87 88 int main() { 89 int i; 90 n = read(); 91 for (i = 1; i <= n; ++i) p[i].get(); 92 alpha = (lf) read() / 180.0 * pi, P = read(); 93 for (i = 1; i <= n; ++i) 94 p[i].rev(-alpha), p[i].x /= P; 95 printf("%.3lf ", min_cover()); 96 return 0; 97 } 98 99 inline int read() { 100 static int x, sgn; 101 static char ch; 102 x = 0, sgn = 1, ch = getchar(); 103 while (ch < '0' || '9' < ch) { 104 if (ch == '-') sgn = -1; 105 ch = getchar(); 106 } 107 while ('0' <= ch && ch <= '9') { 108 x = x * 10 + ch - '0'; 109 ch = getchar(); 110 } 111 return sgn * x; 112 }
(p.s. rank.1液！转圈~转圈~)