三角剖分求多边形面积的交 HDU3060

 //三角剖分求多边形面积的交 HDU3060

 #include <iostream>
 #include <cstdio>
 #include <cstring>
 #include <stack>
 #include <queue>
 #include <cmath>
 #include <algorithm>
 using namespace std;

 const int maxn = ;
 const int maxisn = ;
 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 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 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);
     }
 };

 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 PolygonArea(Point p[], int n) {
     if(n < ) return 0.0;
     double s = p[].y * (p[n - ].x - p[].x);
     p[n] = p[];
     for(int i = ; i < n; ++ i)
         s += p[i].y * (p[i - ].x - p[i + ].x);
     return fabs(s * 0.5);
 }

 double CPIA(Point a[], Point b[], int na, int nb) { //ConvexPolygonIntersectArea
     Point p[maxisn], tmp[maxisn];
     int i, j, tn, sflag, eflag;
     a[na] = a[], b[nb] = b[];
     memcpy(p, b, sizeof(Point) * (nb + ));
     for(i = ; i < na && nb > ; ++ i) {
         sflag = dcmp(a[i].cross(a[i + ], p[]));
         for(j = tn = ; j < nb; ++ j, sflag = eflag) {
             if(sflag >= ) tmp[tn ++] = p[j];
             eflag = dcmp(a[i].cross(a[i + ], p[j + ]));
             if((sflag ^ eflag) == -)
                 tmp[tn ++] = LineCross(a[i], a[i + ], p[j], p[j + ]);
         }
         memcpy(p, tmp, sizeof(Point) * tn);
         nb = tn, p[nb] = p[];
     }
     if(nb < ) return 0.0;
     return PolygonArea(p, nb);
 }

 double SPIA(Point a[], Point b[], int na, int nb) { //SimplePolygonIntersectArea
     int i, j;
     Point t1[], t2[];
     double res = , if_clock_t1, if_clock_t2;
     a[na] = t1[] = a[], b[nb] = t2[] = b[];
     for(i = ; i < na; ++ i) {
         t1[] = a[i - ], t1[] = a[i];
         if_clock_t1 = dcmp(t1[].cross(t1[], t1[]));
         if(if_clock_t1 < ) std::swap(t1[], t1[]);
         for(j = ; j < nb; ++ j) {
             t2[] = b[j - ], t2[] = b[j];
             if_clock_t2 = dcmp(t2[].cross(t2[], t2[]));
             if(if_clock_t2 < ) std::swap(t2[], t2[]);
             res += CPIA(t1, t2, , ) * if_clock_t1 * if_clock_t2;
         }
     }
     return PolygonArea(a, na) + PolygonArea(b, nb) - res;
 }

 Point p1[maxn], p2[maxn];
 int n1, n2;

 int main() {
     int i;
     while(scanf("%d%d", &n1, &n2) != EOF) {
         for(i = ; i < n1; ++ i) scanf("%lf%lf", &p1[i].x, &p1[i].y);
         for(i = ; i < n2; ++ i) scanf("%lf%lf", &p2[i].x, &p2[i].y);
         printf("%.2f\n", SPIA(p1, p2, n1, n2) + eps);
     }
     return ;
 }