poj 1410 Intersection

这个题要考虑直线在正方形的内部；顶点给你的顺序不一定就是左上角到右下角；

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#include<iostream>

#include<cstdio>

#include<cstdlib>

#include<algorithm>

#include<cmath>

#include<queue>

#include<set>

#include<map>

#include<cstring>

#include<vector>

using namespace std;

class Point

{

public:

      double x,y;

};

class Line

{

public:

      Point A,B;    

};

int dcmp( double x )

{

   if( fabs( x ) < 1.0e-8) return 0;

   if( x  < 0 ) return -1;

   return 1;    

}

bool judge( Point p1, Point p2 ,Point q )

{

    double max_x = p1.x > p2.x ? p1.x : p2.x;

    double min_x = p1.x < p2.x ? p1.x : p2.x;

    double max_y = p1.y > p2.y ? p1.y : p2.y;

    double min_y = p1.y <p2.y ? p1.y : p2.y;

    if( dcmp( q.x - min_x ) >=0 && dcmp( max_x - q.x )>=0 ) 

      if( dcmp( q.y - min_y ) >=0 && dcmp( max_y - q.y )>=0 )

        return true;

    return false;    

}

double multi( Point p1, Point p2 , Point q )

{

   return ( p1.x - q.x )*( p2.y - q.y ) - ( p2.x - q.x )*( p1.y - q.y );

}

bool segment( Line L , Line L1 )

{

   int d1 = dcmp(multi( L.A , L.B , L1.A ));

   int d2 = dcmp(multi( L.A, L.B , L1.B ));

   int d3 = dcmp(multi( L1.A, L1.B ,L.A ));

   int d4 = dcmp(multi( L1.A ,L1.B ,L.B ));

   if( d1*d2 < 0 && d3 *d4 < 0 ) return true;

   if( d1 ==0 && judge( L.A , L.B , L1.A )  ) return true;

   if( d2 ==0 && judge( L.A, L.B , L1.B ) ) return true;

   if( d3 ==0 && judge( L1.A, L1.B ,L.A ) ) return true;

   if( d4 ==0 && judge( L1.A , L1.B ,L.B ) ) return true;

   return false;        

}

bool Solve( Line L , Line Re[] )

{

    for( int i = 0 ; i < 4 ; i ++ )

    {

        if( segment( L ,Re[i] ) )

           return true;    

    }    

    return false;

}

bool judge_again( Line L , Point A[] )

{

    double max_x = A[0].x > A[2].x ? A[0].x :A[2].x;

    double min_x = A[0].x < A[2].x ? A[0].x :A[2].x;

    double max_y = A[0].y > A[2].y ? A[0].y :A[2].y;

    double min_y = A[0].y < A[2].y ? A[0].y :A[2].y;

    if( L.A.x >= min_x && L.A.x <= max_x && L.B.x >= min_x && L.B.x <= max_x)

      if( L.A.y >= min_y && L.A.y <= max_y&&L.B.y >=min_y && L.B.y <= max_y )

          return true;

    return false;

}

bool cmp( Point a , Point b )

{

   if( dcmp( a.x - b.x )==0 ) return a.y < b.y;

   return a.x < b.x;    

}

int main(  )

{

    int n;

    while( scanf( "%d",&n )==1 )

    {

      while( n-- )

      { 

         Line L,Re[4];

         Point A[5];

         scanf( "%lf %lf",&L.A.x,&L.A.y );

         scanf( "%lf %lf",&L.B.x,&L.B.y );

         scanf( "%lf %lf %lf %lf",&A[0].x ,&A[0].y ,&A[2].x,&A[2].y );

         if( A[0].y < A[2].y ) swap( A[0] ,A[2] );

         A[1].x = A[2].x ; A[1].y = A[0].y;

         A[3].x = A[0].x ; A[3].y = A[2].y;

         sort( A , A + 4 ,cmp );

         A[4] = A[0];

         for( int i = 0 ; i < 4 ; i ++ )

         {

             Re[i].A = A[i]; Re[i].B = A[i+1];        

         }

         if( Solve( L , Re ) )

         {            

            printf( "T\n" );    

         }

         else 

         {

            if( judge_again( L ,A ) )

                printf( "T\n" );

            else  printf( "F\n" );

         }                 

      }    

    }

    //system( "pause" );

    return 0;

}