两圆面积交：
1 #include <cmath> 2 #include <cstdio> 3 #include <cstdlib> 4 #include <iostream> 5 #define eps 1e-8 6 #define db double 7 #define Pi 3.1415926535 8 using namespace std; 9 10 int dcmp(db x){ 11 if (fabs(x) < eps) return 0; 12 return x < 0 ? -1 : 1; 13 } 14 15 struct Point{ 16 db x, y; 17 }; 18 struct Circle{ 19 db r; 20 Point o; 21 void read() { scanf("%lf%lf%lf", &o.x, &o.y, &r); } 22 }; 23 24 db sqr(db x) { 25 return x*x; 26 } 27 28 db dis(Point a, Point b){ 29 return sqrt(sqr(a.x-b.x) + sqr(a.y-b.y)); 30 } 31 32 db get_Int(Circle c1, Circle c2){ 33 if (c1.r < c2.r) swap(c1, c2); 34 db d = dis(c1.o, c2.o); 35 if (dcmp(d-(c1.r+c2.r)) >= 0) return 0; 36 if (dcmp(d-(c1.r-c2.r)) <= 0) return Pi*sqr(c2.r); 37 db ang1 = acos((sqr(d)+sqr(c1.r)-sqr(c2.r)) / (2*d*c1.r)); 38 db ang2 = acos((sqr(d)+sqr(c2.r)-sqr(c1.r)) / (2*d*c2.r)); 39 db ret = ang1*sqr(c1.r) + ang2*sqr(c2.r) - sin(ang1)*d*c1.r; 40 return ret; 41 } 42 43 int main(){ 44 freopen("cv3273.in", "r", stdin); 45 freopen("cv3273.out", "w", stdout); 46 Circle c1, c2; 47 c1.read(); c2.read(); 48 printf("%.3lf ", get_Int(c1, c2)); 49 return 0; 50 }