HDU 4720 Naive and Silly Muggles (ry)

 

Use a geometric template to find the outer circle, and then judge that the point is not in the circle.

 

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Const double esp = 1e-9; // Point struct Point {double x, y; Point () {} Point (double x, double y) {this-> x = x; this-> y = y;} void read () {scanf (% lf, & x, & y );}}; // Line segment struct Line {Point p [2]; double A, B, C; Line () {} Line (Point a, Point B) {this-> p [0] = a; this-> p [1] = B; A = p [0]. y-p [1]. y; B = p [1]. x-p [0]. x; C =-(A * p [0]. x + B * p [0]. y) ;}}; // Circle struct Circle {Point center; double r; Circle () {} Ci Rcle (Point center, double r) {this-> center = center; this-> r = r ;}}; // triangle struct Tra {Point p [3]; tra () {} Tra (Point a, Point B, Point c) {this-> p [0] = a; this-> p [1] = B; this-> p [2] = c ;}}; // The distance from the dot to the double dis (Point a, Point B) {double dx =. x-B. x; double dy =. y-B. y; return sqrt (dx * dx + dy * dy);} // Point Line symmetric Point P_dc (Line l, Point p) {Point ans; ans. x = p. x-(2 * l. A * (l. A * p. x + l. B * p. y + L. c)/(l. A * l. A + l. B * l. b); ans. y = p. y-(2 * l. B * (l. A * p. x + l. B * p. y + l. c)/(l. A * l. A + l. B * l. b); return ans;} // Triangle Area double Tra_Area (Tra t) {return fabs (t. p [1]. x-t. p [0]. x) * (t. p [2]. y-t. p [0]. y)-(t. p [2]. x-t. p [0]. x) * (t. p [1]. y-t. p [0]. y)/2.0;} // calculates the outer Circle of the triangle, Circle Tra_Cir (Tra t) {Circle ans; double a = dis (t. p [0], t. p [1]); double B = dis (t. p [1], t. p [2]); double c = dis (t. P [2], t. p [0]); ans. r = (a * B * c)/(Tra_Area (t) * 4.0); double xA = t. p [0]. x; double yA = t. p [0]. y; double xB = t. p [1]. x; double yB = t. p [1]. y; double xC = t. p [2]. x; double yC = t. p [2]. y; double c1 = (xA * xA + yA * yA-xB * xB-yB * yB)/2; double c2 = (xA * xA + yA * yA-xC * xC-yC * yC)/2; ans. center. x = (c1*(yA-yC)-c2 * (yA-yB)/(xA-xB) * (yA-yC)-(xA-xC) * (yA-yB); ans. center. y = (c1*(xA-xC)-c2 * (XA-xB)/(yA-yB) * (xA-xC)-(yA-yC) * (xA-xB); return ans ;} // determine the Point in the Circle (including the bool In_Cir (Circle c, Point p) {double d = dis (p, c. center); if (d-c. r> esp) return false; return true;} int t; Point p [4]; bool judge (Circle pc) {if (! In_Cir (pc, p [3]) return true; Circle pc1 = Circle (P_dc (Line (p [0], p [1]), p [3]), pc. r); if (In_Cir (pc1, p [2]) &! In_Cir (pc1, p [3]) return true; pc1 = Circle (P_dc (Line (p [1], p [2]), p [3]), pc. r); if (In_Cir (pc1, p [0]) &! In_Cir (pc1, p [3]) return true; pc1 = Circle (P_dc (Line (p [0], p [2]), p [3]), pc. r); if (In_Cir (pc1, p [1]) &! In_Cir (pc1, p [3]) return true; return false;} int main () {int cas = 0; scanf (% d, & t ); while (t --) {for (int I = 0; I <4; I ++) p [I]. read (); Tra pt = Tra (p [0], p [1], p [2]); Circle pc = Tra_Cir (pt ); printf (Case # % d:, ++ cas); if (judge (pc) printf (Safe); else printf (Danger);} return 0 ;}