poj 2398

叉积+二分

通过叉积来判断点在线段的某侧，找到在点右侧的最左边的边，即可判断点在第几个格子内，可以通过二分来优化查询速度

#include <iostream>
#include <algorithm>
#include <cstdio>
using namespace std;
const int maxn=1000+10;
int n,m,x1,y1,x2,y2;
struct segment
{
	int loc1,loc2;
};
segment s[maxn];
int c[maxn],res[maxn];
bool cmp(segment a,segment b) { return a.loc1<b.loc1; }
int cross(segment ts,int x,int y)
{
	int vx1=ts.loc1-ts.loc2,vy1=y1-y2,vx2=x-ts.loc1,vy2=y-y1;
	return vx1*vy2-vy1*vx2;
}
int main()
{
	while(scanf("%d",&n)&&n)
	{
		scanf("%d%d%d%d%d",&m,&x1,&y1,&x2,&y2);
		int i;
		for(i=1;i<=n;i++)
			scanf("%d%d",&s[i].loc1,&s[i].loc2);
		s[0].loc1=x1;s[0].loc2=x1;
		s[n+1].loc1=x2;s[n+1].loc2=x2;
		sort(s,s+n+2,cmp);
		int x,y;
		memset(c,0,sizeof(c));
		memset(res,0,sizeof(res));
		for(i=0;i<m;i++)
		{
			scanf("%d%d",&x,&y);
			int high=n+2,low=0,mid;
			while(low<high)//找到在点右侧的最左边的边，即可判断点在第几个格子内
			{
				mid=low+(high-low)/2;
				if(cross(s[mid],x,y)>0) high=mid;
				else low=mid+1;
			}
			c[low]++;
		}
		for(i=1;i<=n+1;i++) res[c[i]]++;
		printf("Box\n");
		for(i=1;i<=n+1;i++)
			if(res[i]) printf("%d: %d\n",i,res[i]);
	}
	return 0;
}