HDU 1756 Cupid's Arrow 计算几何

   题目：http://acm.hdu.edu.cn/showproblem.php?pid=1756

   判断点是否在多边形内部

   从点p做一条射线，看射线和多边形的交点有几个,奇数个为相交，偶数个不相交。。。

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<vector>
#include<queue>
#include<math.h>
#include<map>
#include<set>
using namespace std;
#define LL __int64
#define pii pair<int,int>
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
const int MAX=110,INF=200000000;
const double esp=1e-6;
int max(int x,int y){return x>y?x:y;}
int min(int x,int y){return x<y?x:y;}
struct Line{
	int x1,y1,x2,y2;
};
struct Node{
	int x,y;
}nod[MAX];
int chaji(Node &a,Node &b){
	return a.x*b.y-b.x*a.y;
}
int quick(Node &l1,Node &l2,Node &r1,Node &r2);
int las(Node &l1,Node &l2,Node &r1,Node &r2);
int ponls(Node &a,Node &b,Node &p);
int pinply(int num_node,Node nod[],Node &p);
int n,m;
int main()
{
//	freopen("in.txt","r",stdin);
	int i;
	Node p;
	while(~scanf("%d",&n))
	{
		for(i=0;i<n;i++)
			scanf("%d%d",&nod[i].x,&nod[i].y);
		scanf("%d",&m);
		while(m--){
			scanf("%d%d",&p.x,&p.y);
			if(pinply(n,nod,p))
				printf("Yes\n");
			else printf("No\n");
		}
	}
	return 0;
}

int pinply(int num_node,Node nod[],Node &p)
{
	int i,j,cou=0;
	Node ray;
	ray.x=-1,ray.y=p.y;
	for(i=0;i<num_node;i++){
		j=(i+1)%num_node;
		if(ponls(nod[i],nod[j],p))return 0;
		if(nod[i].y!=nod[j].y){
			if(ponls(p,ray,nod[i]) && nod[i].y==max(nod[i].y,nod[j].y))
				cou++;
			else if(ponls(p,ray,nod[j]) && nod[j].y==max(nod[i].y,nod[j].y))
				cou++;
			else if(quick(nod[i],nod[j],p,ray) && las(nod[i],nod[j],p,ray)
				&& las(p,ray,nod[i],nod[j]))
				cou++;
		}
	}
	return cou&1;
}

int ponls(Node &a,Node &b,Node &p)
{
	if( (p.x==a.x && p.y==a.y) || (p.x==b.x && p.y==b.y) )return 2;
	Node r1,r2;
	r1.x=a.x-b.x,r1.y=a.y-b.y;
	r2.x=p.x-b.x,r2.y=p.y-b.y;
	if(!chaji(r1,r2) && p.x>=min(a.x,b.x) && p.x<=max(a.x,b.x) 
		&& p.y>=min(a.y,b.y) && p.y<=max(a.y,b.y))
		return 1;
	return 0;
}

int quick(Node &l1,Node &l2,Node &r1,Node &r2)
{

	if(min(l1.x,l2.x)>max(r1.x,r2.x)
		|| min(l1.y,l2.y)>max(r1.y,r2.y)
		|| max(l1.x,l2.x)<min(r1.x,r2.x)
		|| max(l1.y,l2.y)<min(r1.y,r2.y))
		return 0;
	return 1;
}

int las(Node &l1,Node &l2,Node &r1,Node &r2)
{
	Node a,b,c;
	a.x=l1.x-r1.x;
	a.y=l1.y-r1.y;
	b.x=r2.x-r1.x;
	b.y=r2.y-r1.y;
	c.x=l2.x-r1.x;
	c.y=l2.y-r1.y;
	if( ((a.x*b.y)-(b.x*a.y))*((c.x*b.y)-(b.x*c.y))<0)return 1;
	else return 0;
}