delete pics to save space

1.4196.cpp

@@ -0,0 +1,94 @@
+#include<cstdio>
+#include<cmath>
+#include<algorithm>
+using namespace std;
+struct Point
+{
+	double x,y;
+	Point(double _x=0,double _y=0):x(_x),y(_y) { }
+	inline bool operator<(const Point &b) { return x<b.x||(x==b.x&&y<b.y); }
+};
+typedef Point Vector;
+inline Vector operator+(const Vector &a,const Vector &b) { return Vector(a.x+b.x,a.y+b.y); }
+inline Vector operator-(const Vector &a,const Vector &b) { return Vector(a.x-b.x,a.y-b.y); }
+inline Vector operator*(const Vector &a,double b) { return Vector(a.x*b,a.y*b); }
+inline Vector operator/(const Vector &a,double b) { return Vector(a.x/b,a.y/b); }
+inline double Dot(const Vector &a,const Vector &b) { return a.x*b.x+a.y*b.y; }
+inline double Cross(const Vector &a,const Vector &b) { return a.x*b.y-a.y*b.x; }
+inline double Length(const Vector &a) { return sqrt(Dot(a,a)); }
+const double eps=1e-6;
+inline int dcmp(double x) { return fabs(x)<eps?0:(x>0?1:-1); }
+inline double PolygonArea(Point *p,int n)
+{
+	double area=0;
+	for(int i=1;i<n-1;i++) area+=Cross(p[i]-p[0],p[i+1]-p[0]);
+	return area/2;
+}
+
+struct Line
+{
+	Point P; Vector v; double ang;
+	Line(Point P=Point(),Vector v=Vector()):P(P),v(v) { ang=atan2(v.y,v.x); }
+	inline bool operator<(const Line &b) const { return ang<b.ang; }
+};
+
+inline bool OnLeft(const Line &L,const Point &p) { return dcmp(Cross(L.v,p-L.P))>0; }
+
+inline Point GetLineIntersection(const Line &a,const Line &b)
+{
+	Vector u=a.P-b.P;
+	double t=Cross(b.v,u)/Cross(a.v,b.v);
+	return a.P+a.v*t;
+}
+
+int HalfplaneIntersection(Line *L,int n,Point *poly)
+{
+	sort(L,L+n);
+	int head,tail;
+	Point *p=new Point[n];
+	Line *q=new Line[n];
+	q[head=tail=0]=L[0];
+	for(int i=1;i<n;i++)
+	{
+		while(head<tail&&!OnLeft(L[i],p[tail-1])) tail--;
+		while(head<tail&&!OnLeft(L[i],p[head])) head++;
+		q[++tail]=L[i];
+		if(dcmp(Cross(q[tail].v,q[tail-1].v))==0)
+		{
+			tail--;
+			if(OnLeft(q[tail],L[i].P)) q[tail]=L[i];
+		}
+		if(head<tail) p[tail-1]=GetLineIntersection(q[tail-1],q[tail]);
+	}
+	while(head<tail&&!OnLeft(q[head],p[tail-1])) tail--;
+	if(tail-head<=1) return 0;
+	p[tail]=GetLineIntersection(q[tail],q[head]);
+	
+	int m=0;
+	for(int i=head;i<=tail;i++) poly[m++]=p[i];
+	return m;
+}
+
+const int maxn=25;
+const int maxedge=10*50+7;
+int n,m;
+Point poly[maxn],res[maxedge];
+Line L[maxedge]; int cnt;
+int main()
+{
+#ifdef local
+	freopen("pro.in","r",stdin);
+#endif
+	scanf("%d",&n);
+	for(int i=0;i<n;i++)
+	{
+		scanf("%d",&m);
+		for(int j=0;j<m;j++) scanf("%lf%lf",&poly[j].x,&poly[j].y);
+		for(int j=0;j<m;j++) L[cnt++]=Line(poly[j],poly[(j+1)%m]-poly[j]);
+	}
+	int reslen=HalfplaneIntersection(L,cnt,res);
+	double ans=0;
+	if(reslen>=3) ans=PolygonArea(res,reslen);
+	printf("%.3lf\n",ans);
+	return 0;
+}