poj 3335 /poj 3130/ poj 1474 半平面交 判断核是否存在 / poj1279 半平面交 求核的面积

 /***************
 poj 3335  点序顺时针
 ***************/
 #include <iostream>
 #include <cmath>
 #include <algorithm>
 using namespace std;
 const double eps = 1e-;
 const double maxn = 0x7f7f7f7f;
 int dcmp(double x){
     if(fabs(x)<eps)
         return ;
     else
         return x<?-:;
 }
 struct point {
     double x,y;
     point (double x=,double y =):x(x),y(y){}
 };
 point p[];
 typedef point Vector;

 struct polygon{
     point p[];
     int Size;
 };

 struct line{
     point fir,sec;
     line(point a = point(),point b = point()){
         fir = a;
         sec = b;
     }
 };

 Vector operator -(point a,point b){
     return Vector(a.x-b.x,a.y-b.y);
 }

 Vector operator *(Vector a,double p){
     return Vector (a.x*p,a.y*p);
 }
 Vector operator + (Vector a,Vector b){
     return Vector (a.x+b.x,a.y+b.y);
 }

 double cross(Vector a,Vector b){
     return a.x*b.y-a.y*b.x;
 }

 double dot(Vector a,Vector b){
     return a.x*b.x+a.y*b.y;
 }

 point getLineIntersection(point p,Vector v,point q,Vector w){
     Vector u = p-q;
     double t = cross(w,u)/cross(v,w);
     return p+v*t;
 }

 bool onsegment(point p,point a1,point a2){
     return dcmp(cross(a1-p,a2-p))==&&dcmp(dot(a1-p,a2-p))<;
 }

 polygon cutploygon(polygon poly,line ln){
     polygon newploy;
     int m=;
     int n = poly.Size;
     point a = ln.fir,b = ln.sec;
     for(int i=;i<n;i++){
         point c = poly.p[i];
         point d = poly.p[(i+)%n];
         double cc = cross(b-a,c-a);
         double dd = cross(b-a,d-a);
         if(cc>=)
             newploy.p[m++] = c;
         if(cc*dd<)
             newploy.p[m++] = getLineIntersection(a,b-a,c,d-c);
     }
     newploy.Size = m;
     return newploy;
 }

 int main()
 {
     int t;
     cin>>t;
     int n;
     while(t--){
         cin>>n;
         for(int i=;i<n;i++)
             cin>>p[i].x>>p[i].y;
         polygon poly;
         poly.Size = ;
         poly.p[].x = -maxn;
         poly.p[].y = -maxn;
         poly.p[].x = maxn;
         poly.p[].y = -maxn;
         poly.p[].x = maxn;
         poly.p[].y = maxn;
         poly.p[].x = -maxn;
         poly.p[].y = maxn;
         bool flag = true;
         for(int i=;i<=n;i++){
             line ln;
             ln.fir = p[i%n];
             ln.sec = p[i-];
             poly = cutploygon(poly,ln);
             if(poly.Size==){
                 flag = false;
                 break;
             }
         }
         if(!flag)
             cout<<"NO"<<endl;
         else
             cout<<"YES"<<endl;
     }
     return ;
 }

 /****************************************/
 poj   点序逆时针
 /****************************************/

 #include <iostream>
 #include <cmath>
 #include <algorithm>
 using namespace std;
 const double eps = 1e-;
 const double maxn = 0x7f7f7f7f;
 int dcmp(double x){
     if(fabs(x)<eps)
         return ;
     else
         return x<?-:;
 }
 struct point {
     double x,y;
     point (double x=,double y =):x(x),y(y){}
 };
 point p[];
 typedef point Vector;

 struct polygon{
     point p[];
     int Size;
 };

 struct line{
     point fir,sec;
     line(point a = point(),point b = point()){
         fir = a;
         sec = b;
     }
 };

 Vector operator -(point a,point b){
     return Vector(a.x-b.x,a.y-b.y);
 }

 Vector operator *(Vector a,double p){
     return Vector (a.x*p,a.y*p);
 }
 Vector operator + (Vector a,Vector b){
     return Vector (a.x+b.x,a.y+b.y);
 }

 double cross(Vector a,Vector b){
     return a.x*b.y-a.y*b.x;
 }

 double dot(Vector a,Vector b){
     return a.x*b.x+a.y*b.y;
 }

 point getLineIntersection(point p,Vector v,point q,Vector w){
     Vector u = p-q;
     double t = cross(w,u)/cross(v,w);
     return p+v*t;
 }

 bool onsegment(point p,point a1,point a2){
     return dcmp(cross(a1-p,a2-p))==&&dcmp(dot(a1-p,a2-p))<;
 }

 polygon cutploygon(polygon poly,line ln){
     polygon newploy;
     int m=;
     int n = poly.Size;
     point a = ln.fir,b = ln.sec;
     for(int i=;i<n;i++){
         point c = poly.p[i];
         point d = poly.p[(i+)%n];
         double cc = cross(b-a,c-a);
         double dd = cross(b-a,d-a);
         if(cc>=)
             newploy.p[m++] = c;
         if(cc*dd<)
             newploy.p[m++] = getLineIntersection(a,b-a,c,d-c);
     }
     newploy.Size = m;
     return newploy;
 }

 int main()
 {
     int n;
     while(cin>>n&&n){
         for(int i=;i<n;i++)
             cin>>p[i].x>>p[i].y;
         polygon poly;
         poly.Size = ;
         poly.p[].x = -maxn;
         poly.p[].y = -maxn;
         poly.p[].x = maxn;
         poly.p[].y = -maxn;
         poly.p[].x = maxn;
         poly.p[].y = maxn;
         poly.p[].x = -maxn;
         poly.p[].y = maxn;
         bool flag = true;
         for(int i=;i<n;i++){
             line ln;
             ln.fir = p[i%n];
             ln.sec = p[(i+)%n];
             poly = cutploygon(poly,ln);
             if(poly.Size==){
                 flag = false;
                 break;
             }
         }
         if(!flag)
             cout<<""<<endl;
         else
             cout<<""<<endl;
     }
     return ;
 }

 /*************************************/
 poj    点序顺时针
 /*************************************/
 #include <iostream>
 #include <cmath>
 #include <algorithm>
 using namespace std;
 const double eps = 1e-;
 const double maxn = 0x7f7f7f7f;
 int dcmp(double x){
     if(fabs(x)<eps)
         return ;
     else
         return x<?-:;
 }
 struct point {
     double x,y;
     point (double x=,double y =):x(x),y(y){}
 };
 point p[];
 typedef point Vector;

 struct polygon{
     point p[];
     int Size;
 };

 struct line{
     point fir,sec;
     line(point a = point(),point b = point()){
         fir = a;
         sec = b;
     }
 };

 Vector operator -(point a,point b){
     return Vector(a.x-b.x,a.y-b.y);
 }

 Vector operator *(Vector a,double p){
     return Vector (a.x*p,a.y*p);
 }
 Vector operator + (Vector a,Vector b){
     return Vector (a.x+b.x,a.y+b.y);
 }

 double cross(Vector a,Vector b){
     return a.x*b.y-a.y*b.x;
 }

 double dot(Vector a,Vector b){
     return a.x*b.x+a.y*b.y;
 }

 point getLineIntersection(point p,Vector v,point q,Vector w){
     Vector u = p-q;
     double t = cross(w,u)/cross(v,w);
     return p+v*t;
 }

 bool onsegment(point p,point a1,point a2){
     return dcmp(cross(a1-p,a2-p))==&&dcmp(dot(a1-p,a2-p))<;
 }

 polygon cutploygon(polygon poly,line ln){
     polygon newploy;
     int m=;
     int n = poly.Size;
     point a = ln.fir,b = ln.sec;
     for(int i=;i<n;i++){
         point c = poly.p[i];
         point d = poly.p[(i+)%n];
         double cc = cross(b-a,c-a);
         double dd = cross(b-a,d-a);
         if(cc>=)
             newploy.p[m++] = c;
         if(cc*dd<)
             newploy.p[m++] = getLineIntersection(a,b-a,c,d-c);
     }
     newploy.Size = m;
     return newploy;
 }

 int main()
 {
     int n;
     int cnt =;
     while(cin>>n&&n){
         for(int i=;i<n;i++)
             cin>>p[i].x>>p[i].y;
         polygon poly;
         poly.Size = ;
         poly.p[].x = -maxn;
         poly.p[].y = -maxn;
         poly.p[].x = maxn;
         poly.p[].y = -maxn;
         poly.p[].x = maxn;
         poly.p[].y = maxn;
         poly.p[].x = -maxn;
         poly.p[].y = maxn;
         bool flag = true;
         for(int i=;i<=n;i++){
             line ln;
             ln.fir = p[i%n];
             ln.sec = p[i-];
             poly = cutploygon(poly,ln);
             if(poly.Size==){
                 flag = false;
                 break;
             }
         }
         //cout<<poly.Size<<endl;
         cout<<"Floor #"<<cnt++<<endl;
         if(!flag)
             cout<<"Surveillance is impossible."<<endl;
         else
             cout<<"Surveillance is possible."<<endl;
         cout<<endl;
     }
     return ;
 }

 /**********************************
 poj 1279  点序顺时针
 **********************************/
 #include <iostream>
 #include <cmath>
 #include <algorithm>
 #include <cstdio>
 using namespace std;
 const double eps = 1e-;
 const double maxn = 0x7f7f7f7f;
 int dcmp(double x){
     if(fabs(x)<eps)
         return ;
     else
         return x<?-:;
 }
 struct point {
     double x,y;
     point (double x=,double y =):x(x),y(y){}
 };
 point p[];
 typedef point Vector;

 struct polygon{
     point p[];
     int Size;
 };

 struct line{
     point fir,sec;
     line(point a = point(),point b = point()){
         fir = a;
         sec = b;
     }
 };

 Vector operator -(point a,point b){
     return Vector(a.x-b.x,a.y-b.y);
 }

 Vector operator *(Vector a,double p){
     return Vector (a.x*p,a.y*p);
 }
 Vector operator + (Vector a,Vector b){
     return Vector (a.x+b.x,a.y+b.y);
 }

 double cross(Vector a,Vector b){
     return a.x*b.y-a.y*b.x;
 }

 double dot(Vector a,Vector b){
     return a.x*b.x+a.y*b.y;
 }

 point getLineIntersection(point p,Vector v,point q,Vector w){
     Vector u = p-q;
     double t = cross(w,u)/cross(v,w);
     return p+v*t;
 }

 bool onsegment(point p,point a1,point a2){
     return dcmp(cross(a1-p,a2-p))==&&dcmp(dot(a1-p,a2-p))<;
 }

 polygon cutploygon(polygon poly,line ln){
     polygon newploy;
     int m=;
     int n = poly.Size;
     point a = ln.fir,b = ln.sec;
     for(int i=;i<n;i++){
         point c = poly.p[i];
         point d = poly.p[(i+)%n];
         double cc = cross(b-a,c-a);
         double dd = cross(b-a,d-a);
         if(cc>=)
             newploy.p[m++] = c;
         if(cc*dd<)
             newploy.p[m++] = getLineIntersection(a,b-a,c,d-c);
     }
     newploy.Size = m;
     return newploy;
 }

 double polyArea(point *p,int n){
     double area =;
     for(int i=;i<n-;i++){
         area += cross(p[i]-p[],p[i+]-p[]);
     }
     return area/;
 }

 int main()
 {
     int t;
     cin>>t;
     int n;
     while(t--){
         cin>>n;
         for(int i=;i<n;i++)
             cin>>p[i].x>>p[i].y;
         polygon poly;
         poly.Size = ;
         poly.p[].x = -maxn;
         poly.p[].y = -maxn;
         poly.p[].x = maxn;
         poly.p[].y = -maxn;
         poly.p[].x = maxn;
         poly.p[].y = maxn;
         poly.p[].x = -maxn;
         poly.p[].y = maxn;
         bool flag = true;
         for(int i=;i<=n;i++){
             line ln;
             ln.fir = p[i%n];
             ln.sec = p[i-];
             poly = cutploygon(poly,ln);
             if(poly.Size==){
                 flag = false;
                 break;
             }
         }
         double res;
         if(!flag)
             res =;
         else{
             res = polyArea(poly.p,poly.Size);
         }
         printf("%.2lf\n",res);
     }
     return ;
 }