ZOJ 1081 Points Within(点在多边形内判定)
http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemId=81
题意:
给你一个简单多边形,然后给你m个点,问你这m个点分别是否在多边形内部(包括边界上)?
分析:
直接用刘汝佳的判定点在多边形内部的模板即可.不再赘述了.
AC代码:
#include<cstdio> #include<cmath> #include<cstring> using namespace std; const double eps=1e-10; const int maxn=1000+10; int dcmp(double x) { if(fabs(x)<eps) return 0; return x<0?-1:1; } struct Point { double x,y; Point(){} Point(double x,double y):x(x),y(y){} }; typedef Point Vector; Vector operator-(Point A,Point B) { return Vector(A.x-B.x,A.y-B.y); } double Dot(Vector A,Vector B) { return A.x*B.x+A.y*B.y; } double Cross(Vector A,Vector B) { return A.x*B.y-A.y*B.x; } bool InSegment(Point P,Point A,Point B) { return dcmp(Cross(A-B,P-A))==0 && dcmp(Dot(A-P,B-P))<=0; } bool PointInPolygon(Point p,Point* poly,int n) { int wn=0; for(int i=0;i<n;++i) { if(InSegment(p,poly[i],poly[(i+1)%n])) return true; int k=dcmp( Cross(poly[(i+1)%n]-poly[i], p-poly[i]) ); int d1=dcmp(poly[i].y-p.y); int d2=dcmp(poly[(i+1)%n].y-p.y); if(k>0 && d1<=0 && d2>0) ++wn; if(k<0 && d2<=0 && d1>0) --wn; } if(wn!=0) return true; return false; } int main() { int n,m,kase=0; while(scanf("%d",&n)==1 && n) { if(kase>0) printf("\n"); printf("Problem %d:\n",++kase); scanf("%d",&m); Point poly[maxn]; for(int i=0;i<n;++i) { scanf("%lf%lf",&poly[i].x,&poly[i].y); } for(int i=0;i<m;++i) { Point p; scanf("%lf%lf",&p.x,&p.y); if(PointInPolygon(p,poly,n)) printf("Within\n"); else printf("Outside\n"); } } return 0; }