poj2540Hotter Colder(半平面交）

链接

根据距离可以列得直线方程，附上初始矩形的四个顶点，依次用直线切割。

 #include<iostream>
 #include <stdio.h>
 #include <math.h>
 #include<cstring>
 #include<algorithm>
 #define eps 1e-8
 using namespace std;
 const int MAXN=;
 int m;
 double r,tx,ty,ans;
 int cCnt,curCnt;//此时cCnt为最终切割得到的多边形的顶点数、暂存顶点个数
 struct point
 {
     double x,y;
     point(double x=,double y=):x(x),y(y) {}
 };
 point points[MAXN],p[MAXN],q[MAXN];//读入的多边形的顶点（顺时针）、p为存放最终切割得到的多边形顶点的数组、暂存核的顶点
 void getline(point x,point y,double &a,double &b,double   &c) //两点x、y确定一条直线a、b、c为其系数
 {
     a = y.y - x.y;
     b = x.x - y.x;
     c = y.x * x.y - x.x * y.y;
 }
 void initial()
 {
     for(int i = ; i <= m; ++i)p[i] = points[i];
     p[m+] = p[];
     p[] = p[m];
     cCnt = m;//cCnt为最终切割得到的多边形的顶点数，将其初始化为多边形的顶点的个数
 }
 point intersect(point x,point y,double a,double b,double c) //求x、y形成的直线与已知直线a、b、c、的交点
 {
     //cout<<a<<" "<<b<<" "<<c<<endl;
     double u = fabs(a * x.x + b * x.y + c);
     double v = fabs(a * y.x + b * y.y + c);
     // cout<<u<<" "<<v<<endl;
     point pt;
     pt.x=(x.x * v + y.x * u) / (u + v);
     pt.y=(x.y * v + y.y * u) / (u + v);//cout<<pt.x<<" -"<<pt.y<<" "<<x.x<<" "<<y.x<<endl;
     return  pt;
 }
 void cut(double a,double b ,double c)
 {
     curCnt = ;
     for(int i = ; i <= cCnt; ++i)
     {
         if(a*p[i].x + b*p[i].y + c > -eps)q[++curCnt] = p[i];
         else
         {
             if(a*p[i-].x + b*p[i-].y + c > eps)
             {
                 q[++curCnt] = intersect(p[i-],p[i],a,b,c);
             }
             if(a*p[i+].x + b*p[i+].y + c > eps) //原理同上
             {
                 q[++curCnt] = intersect(p[i],p[i+],a,b,c);
             }
         }
         //cout<<q[curCnt].x<<" --"<<q[curCnt].y<<" "<<i<<" "<<p[i].x<<" "<<p[i].y<<endl;
     }
     for(int i = ; i <= curCnt; ++i)p[i] = q[i];
     p[curCnt+] = q[];
     p[] = p[curCnt];
     cCnt = curCnt;
 }
 int dcmp(double x)
 {
     if(fabs(x)<eps) return ;
     return x<?-:;
 }
 void solve(double x,double y,int flag)
 {
     double a,b,c;
     if(flag == )
     {
         a = -*x+*tx,b = -*y+*ty,c = x*x+y*y-tx*tx-ty*ty;
     }
     else if(flag==)
     {
         a = *x-*tx,b = *y-*ty,c = tx*tx+ty*ty-x*x-y*y;
     }
 //    if(dcmp(a)==0&&dcmp(b)==0&&dcmp(c)<=0)
 //    {
 //        ans = 0;
 //        return ;
 //    }
     cut(a,b,c);
 }
 int main()
 {
     points[] = point(,);
     points[] = point(,);
     points[] = point(,);
     points[] = point(,);
     p[] = p[];
     m = ;
     tx = ,ty=;
     char s[];
     double x,y;
     initial();
     while(scanf("%lf%lf%s",&x,&y,s)!=EOF)
     {
         int flag;
         if(strcmp(s,"Colder")==||strcmp(s,"Same")==)solve(x,y,);
         if(strcmp(s,"Hotter")==||strcmp(s,"Same")==)solve(x,y,);
         tx = x,ty=y;
         double area = ;
         for(int i = ; i <= cCnt; ++i)
         {
             //cout<<p[i].x<<" "<<p[i].y<<endl;
             area += p[i].x * p[i + ].y - p[i + ].x * p[i].y;
         }
         area = fabs(area / 2.0);
         ans = area;
         printf("%.2f\n",ans);
     }
 }