poj 2540 Hotter Colder

一道半平面相交的题目：

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#include<iostream>

#include<cstdio>

#include<cstdlib>

#include<algorithm>

#include<cmath>

#include<queue>

#include<set>

#include<map>

#include<cstring>

#include<vector>

#include<string>

#define LL long long

using namespace std;

class Point

{

public:

      double x,y;

      Point(){}

      Point( double xx , double yy ):x(xx),y(yy){}

}p[124],q[124];

void Init( Point &pre )

{

    pre = Point( 0 , 0 );

    p[1] = Point( 0 , 0 );

    p[2] = Point( 0 , 10 );

    p[3] = Point( 10 , 10 );

    p[4] = Point( 10 , 0 );

    p[5] = p[1];

    p[0] = p[4];

}

void Get_line( Point pre, Point cur , double &A, double &B, double &C)

{

    Point a = Point( (pre.x + cur.x)/2.0 , ( pre.y + cur.y )/2.0 );

    A = cur.x - pre.x;

    B = cur.y - pre.y;

    C = -A*a.x - B*a.y;    

}

Point Get_point( Point a,Point b, double A,double B,double C )

{

     double u = fabs( A*a.x + B*a.y + C );

    double v = fabs( A*b.x + B*b.y + C );

    Point ans;

    ans.x = ( u*b.x + v*a.x )/(u+v);

    ans.y = ( u*b.y + v*a.y )/(u+v);

    return ans;    

}

int Solve( int n ,double A,double B,double C)

{

    int m = 0;

       for( int i = 1 ; i <= n ; i ++ )

       {

       if( A*p[i].x + B*p[i].y + C > 0 )

           q[++m] = p[i];

       else

       {

           if( A*p[i-1].x + B*p[i-1].y + C > 0 )

               q[++m] = Get_point( p[i] , p[i-1] ,A,B,C );

           if(A*p[i+1].x + B*p[i+1].y + C > 0)

                  q[++m] = Get_point( p[i] , p[i+1] ,A,B,C );         

       }        

    }

    for( int i =1 ; i <= m; i ++ )

         p[i] = q[i];

    p[m+1] = p[1];

    p[0] = p[m];

    return m;

}

double Area( int n )

{

      double area=0;

      p[n+1] = p[1];

      for( int i = 1; i <= n ; i ++ )

           area += p[i].x*p[i+1].y - p[i].y*p[i+1].x;

      return fabs( area/2.0 );    

}

int main(  )

{

    Point pre,cur;

    bool flag = false;

    char str[12];

    double  A,B,C;

    int n = 4;

    Init( pre );

      while( scanf( "%lf%lf%s",&cur.x,&cur.y,str )==3 )

      {

         if( !flag )

         {

             Get_line( pre , cur , A,B,C );

             if( str[0] == 'C' ) 

             {

                 if( A*pre.x + B*pre.y + C < 0 )

                 {

                     A = -A; B = -B ; C = -C; 

                 }             

             }

             else if( str[0] == 'H' )

                  {

                      if( A*cur.x + B*cur.y + C < 0 )

                      {

                         A = -A ; B = -B ; C = -C;        

                      }

                  }

              else {flag = true;puts( "0.00" );continue;}

                n =  Solve( n ,A ,B ,C );    

             printf("%.2f\n",Area( n ) );

             pre = cur;    

         }

         else puts( "0.00" );          

    }

    //system( "pause" );

    return 0;

}