计算几何模板
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
#include<algorithm> const double eps = 1e-;
const double pi = acos(-1.0); int dcmp(double x)
{
if(x > eps) return ;
return x < -eps ? - : ;
} struct Point
{
double x, y;
Point()
{
x = y = ;
}
Point(double a, double b)
{
x = a, y = b;
}
inline void read()
{
scanf("%lf%lf", &x, &y);
}
inline Point operator-(const Point &b)const
{
return Point(x - b.x, y - b.y);
}
inline Point operator+(const Point &b)const
{
return Point(x + b.x, y + b.y);
}
inline Point operator*(const double &b)const
{
return Point(x * b, y * b);
}
inline double dot(const Point &b)const
{
return x * b.x + y * b.y;
}
inline double cross(const Point &b, const Point &c)const
{
return (b.x - x) * (c.y - y) - (c.x - x) * (b.y - y);
}
inline double Dis(const Point &b)const
{
return sqrt((*this - b).dot(*this - b));
}
inline bool InLine(const Point &b, const Point &c)const//三点共线
{
return !dcmp(cross(b, c));
}
inline bool OnSeg(const Point &b, const Point &c)const//点在线段上，包括端点
{
return InLine(b, c) && (*this - c).dot(*this - b) < eps;
}
}; inline double min(double a, double b)
{
return a < b ? a : b;
}
inline double max(double a, double b)
{
return a > b ? a : b;
}
inline double Sqr(double x)
{
return x * x;
}
inline double Sqr(const Point &p)
{
return p.dot(p);
} Point LineCross(const Point &a, const Point &b, const Point &c, const Point &d)
{
double u = a.cross(b, c), v = b.cross(a, d);
return Point((c.x * v + d.x * u) / (u + v), (c.y * v + d.y * u) / (u + v));
} double LineCrossCircle(const Point &a, const Point &b, const Point &r,
double R, Point &p1, Point &p2)
{
Point fp = LineCross(r, Point(r.x + a.y - b.y, r.y + b.x - a.x), a, b);
double rtol = r.Dis(fp);
double rtos = fp.OnSeg(a, b) ? rtol : min(r.Dis(a), r.Dis(b));
double atob = a.Dis(b);
double fptoe = sqrt(R * R - rtol * rtol) / atob;
if(rtos > R - eps) return rtos;
p1 = fp + (a - b) * fptoe;
p2 = fp + (b - a) * fptoe;
return rtos;
} double SectorArea(const Point &r, const Point &a, const Point &b, double R)
//不大于180度扇形面积，r->a->b逆时针
{
double A2 = Sqr(r - a), B2 = Sqr(r - b), C2 = Sqr(a - b);
return R * R * acos((A2 + B2 - C2) * 0.5 / sqrt(A2) / sqrt(B2)) * 0.5;
} double TACIA(const Point &r, const Point &a, const Point &b, double R)
//TriangleAndCircleIntersectArea，逆时针，r为圆心
{
double adis = r.Dis(a), bdis = r.Dis(b);
if(adis < R + eps && bdis < R + eps) return r.cross(a, b) * 0.5;
Point ta, tb;
if(r.InLine(a, b)) return 0.0;
double rtos = LineCrossCircle(a, b, r, R, ta, tb);
if(rtos > R - eps) return SectorArea(r, a, b, R);
if(adis < R + eps) return r.cross(a, tb) * 0.5 + SectorArea(r, tb, b, R);
if(bdis < R + eps) return r.cross(ta, b) * 0.5 + SectorArea(r, a, ta, R);
return r.cross(ta, tb) * 0.5 +
SectorArea(r, a, ta, R) + SectorArea(r, tb, b, R);
} const int N = ; Point p[N]; double SPICA(int n, Point r, double R)//SimplePolygonIntersectCircleArea
{
int i;
double res = , if_clock_t;
for(i = ; i < n; ++ i)
{
if_clock_t = dcmp(r.cross(p[i], p[(i + ) % n]));
if(if_clock_t < ) res -= TACIA(r, p[(i + ) % n], p[i], R);
else res += TACIA(r, p[i], p[(i + ) % n], R);
}
return fabs(res);
} double r; int main()
{
while (~scanf("%lf%lf", &p[].x, &p[].y))
{
for (int i = ; i < ; i++)
p[i].read();
scanf("%lf", &r);
printf("%.2f\n", SPICA(, p[], r));
}
return ;
}