poj 2074 Line of Sight

#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<cstring>
using namespace std;
class Line
{
public:
double x1,x2,y;
}line[224];
Line house,pro;
int dcmp( double x )
{
if( fabs( x ) < 1.0e-12 ) return 0;
if( x < 0 ) return -1;
return 1;
}
bool cmp( Line a, Line b )
{
if( a.x1 < b.x1 ) return true;
else if( dcmp( a.x1 - b.x1)==0 && a.y < b.y ) return true;
return false;
}
double Max( double a , double b)
{
return a > b ? a : b;
}
double Solve( int n )
{
Line L[224]={0};
double A1,B,A2;
for( int i = 0 ; i < n ; i ++ )
{
A1 = house.x2 - line[i].x1;
B = house.y - line[i].y;
A2 = house.x1 - line[i].x2;
L[i].x1 = ( pro.y - house.y )*A1/B + house.x2;
L[i].x2 = ( pro.y - house.y )*A2/B + house.x1;
}
sort( L , L + n , cmp );
double ans = 0;
if( L[0].x1 > pro.x1 ) ans = L[0].x1 - pro.x1;
double t = L[0].x2;
for( int i = 1 ; i < n ; i ++ )
{
if( L[i].x1 <= t ) t = Max( t , L[i].x2 );
else
{
ans = Max( ans , L[i].x1 - t );
t = L[i].x2;
}
}
ans = Max( ans , pro.x2 - t );
return ans;
}
int main(  )
{
while( scanf( "%lf %lf %lf",&house.x1,&house.x2,&house.y )==3)
{
int n,flag = 0,cnt=0;
if(dcmp(house.x1)==0&&dcmp(house.x2)==0&&dcmp(house.y)==0 ) break;
scanf( "%lf %lf %lf",&pro.x1, &pro.x2,&pro.y );
scanf( "%d",&n );
for( int i = 0; i < n ; i++ )
{
scanf( "%lf %lf %lf",&line[i].x1,&line[i].x2,&line[i].y );
if( dcmp(line[i].y - house.y) ==0 )
{
if( dcmp( line[i].x1 - house.x2 ) <= 0 && dcmp( line[i].x2 - house.x1 ) >= 0 )
flag = 1;
}
else if( line[i].y < house.y && line[i].y > pro.y )line[cnt++] = line[i];
}
if( flag ) printf( "No View\n" );
else
{
if( cnt == 0 ) printf( "%.2f\n",pro.x2-pro.x1 );
else
{
sort( line , line + cnt , cmp );
double view = Solve( cnt );
if( dcmp( view )==0 ) printf( "No View\n" );
else printf( "%.2f\n",view );
}
}
}
//system( "pause" );
return 0;
}