#include #include #include using namespace std; struct Point { double x, y; Point(double a = 0.0, double b = 0.0) { x = a; y = b; } }; double LenghtLine(Point A, Point B) { return sqrt(abs((B.x - A.x)*(B.x - A.x)) + abs((B.y - A.y)*(B.y - A.y))); } double TriangleArea(Point A, Point B, Point C) { double a = LenghtLine(A, B); double b = LenghtLine(B, C); double c = LenghtLine(C, A); double p = (a + b + c) / 2; return sqrt(p*(p - a)*(p - b)*(p - c)); } bool PointInCircle(vector &P, Point Center, double R) { for (size_t i = 0; i < P.size(); i++) { if (LenghtLine(P[i], Center) > R) return false; } return true; } double circle(vector P) { double minR = INT8_MAX; double R; Point C; Point minC; for (size_t i = 0; i < P.size() - 2; i++) for (size_t j = i+1; j < P.size(); j++) for (size_t k = j+1; k < P.size(); k++) { C.x = -0.5 * ((P[i].y*(P[j].x*P[j].x + P[j].y*P[j].y - P[k].x*P[k].x - P[k].y*P[k].y) + P[j].y*(P[k].x*P[k].x + P[k].y*P[k].y - P[i].x*P[i].x - P[i].y*P[i].y) + P[k].y*(P[i].x*P[i].x + P[i].y*P[i].y - P[j].x*P[j].x - P[j].y*P[j].y)) / (P[i].x*(P[j].y - P[k].y) + P[j].x*(P[k].y - P[i].y) + P[k].x*(P[i].y - P[j].y) )); C.y = 0.5 * ((P[i].x*(P[j].x*P[j].x + P[j].y*P[j].y - P[k].x*P[k].x - P[k].y*P[k].y) + P[j].x*(P[k].x*P[k].x + P[k].y*P[k].y - P[i].x*P[i].x - P[i].y*P[i].y) + P[k].x*(P[i].x*P[i].x + P[i].y*P[i].y - P[j].x*P[j].x - P[j].y*P[j].y)) / (P[i].x*(P[j].y - P[k].y) + P[j].x*(P[k].y - P[i].y) + P[k].x*(P[i].y - P[j].y) )); R = (LenghtLine(P[i], P[j]) * LenghtLine(P[j], P[k]) * LenghtLine(P[k], P[i])) / (4 * TriangleArea(P[i], P[j], P[k])); if (!PointInCircle(P, C, R)) { continue; } if (R <= minR) { minR = R; minC = C; } } for (size_t i = 0; i < P.size() - 1; i++) for (size_t j = i + 1; j < P.size(); j++) { C.x = (P[i].x + P[j].x) / 2; C.y = (P[i].y + P[j].y) / 2; R = LenghtLine(C, P[i]); if (!PointInCircle(P, C, R)) { continue; } if (R <= minR) { minR = R; minC = C; } } cout << minC.x << " " << minC.y << endl; return minR; } void test() { vector Pv(5); Pv.push_back(Point(0,0)); Pv.push_back(Point(1,3)); Pv.push_back(Point(4,1)); Pv.push_back(Point(5,4)); Pv.push_back(Point(3,-2)); cout << circle(Pv) << endl; } void test2() { vector Pv(4); Pv.push_back(Point(0,0)); Pv.push_back(Point(0,2)); Pv.push_back(Point(2,2)); Pv.push_back(Point(2,0)); cout << circle(Pv) << endl; } void test3() { vector Pv(3); Pv.push_back(Point(0.5,1)); Pv.push_back(Point(3.5,3)); Pv.push_back(Point(2.5,0)); cout << circle(Pv) << endl; } int main() { test(); cout << endl; test2(); cout << endl; test3(); return 0; }