HDU1632+半平面交

模板题

题意：给定两个凸多边形，求出合并后的面积，这个合并后的面积不包括重叠部分。

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>
#include<algorithm>
using namespace std;
const int maxn = 155;
const int maxm = 155;
const double eps = 1e-8;
const double pi = acos(-1.0);
struct Point{
    double x,y;
};
struct Line{
    Point a,b;
};
Point pnt1[ maxn ],res[ maxm ],pnt2[ maxn ],tp[ maxm ];
double xmult( Point op,Point sp,Point ep ){
    return (sp.x-op.x)*(ep.y-op.y)-(sp.y-op.y)*(ep.x-op.x);
}
double dist( Point a,Point b ){
    return sqrt( (a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y) );
}
void Get_equation( Point p1,Point p2,double &a,double &b,double &c ){
    a = p2.y-p1.y;
    b = p1.x-p2.x;
    c = p2.x*p1.y-p1.x*p2.y;
}//直线方程
Point Intersection( Point p1,Point p2,double a,double b,double c ){
    double u = fabs( a*p1.x+b*p1.y+c );
    double v = fabs( a*p2.x+b*p2.y+c );
    Point tt;
    tt.x = (p1.x*v+p2.x*u)/(u+v);
    tt.y = (p1.y*v+p2.y*u)/(u+v);
    return tt;
}//交点、按照三角比例求出交点
double GetArea( Point p[],int n ){
    double sum = 0;
    for( int i=2;i<n;i++ ){
        sum += xmult( p[1],p[i],p[i+1] );
    }
    return -sum/2.0;
}//面积，顺时针为正
void cut( double a,double b,double c,int &cnt ){
    int temp = 0;
    for( int i=1;i<=cnt;i++ ){
        if( a*res[i].x+b*res[i].y+c>-eps ){//>=0
            tp[ ++temp ] = res[i];
        }
        else{
            if( a*res[i-1].x+b*res[i-1].y+c>eps ){
                tp[ ++temp ] = Intersection( res[i-1],res[i],a,b,c );
            }
            if( a*res[i+1].x+b*res[i+1].y+c>eps ){
                tp[ ++temp ] = Intersection( res[i],res[i+1],a,b,c );
            }
        }
    }
    for( int i=1;i<=temp;i++ )
        res[i] = tp[i];
    res[ 0 ] = res[ temp ];
    res[ temp+1 ] = res[ 1 ];
    cnt = temp;
}

int main(){
    int m,n;
    while( scanf("%d",&n)==1,n ){
        for( int i=1;i<=n;i++ ){
            scanf("%lf%lf",&pnt1[i].x,&pnt1[i].y);
        }
        scanf("%d",&m);
        for( int i=1;i<=m;i++ ){
            scanf("%lf%lf",&pnt2[i].x,&pnt2[i].y);
        }
        double sumArea1,sumArea2,Area;
        sumArea1 = GetArea( pnt1,n );
        sumArea2 = GetArea( pnt2,m );
        if( sumArea1<eps ){
            reverse( pnt1+1,pnt1+1+n );
        }
        pnt1[ 0 ] = pnt1[ n ];
        pnt1[ n+1 ] = pnt1[ 1 ];
        if( sumArea2<eps ){
            reverse( pnt2+1,pnt2+1+m );
        }
        pnt2[ 0 ] = pnt2[ m ];
        pnt2[ m+1 ] = pnt2[ 1 ];
        for( int i=0;i<=n+1;i++ ){
            res[i] = pnt1[i];
        }
        int cnt = n;
        for( int i=1;i<=m;i++ ){
            double a,b,c;  
            Get_equation( pnt2[i],pnt2[i+1],a,b,c );  
            cut(a,b,c,cnt);  
        }  
        Area = GetArea( res,cnt );
        double ans = fabs(sumArea1)+fabs(sumArea2)-2.0*fabs(Area);
        printf("%8.2lf",ans);
    }
    puts("");
    return 0;
}