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 ){//>=0tp[ ++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;}