poj2318 TOYS

传送门
用叉积判断在直线的哪一侧，二分答案。

#include<cstdio>
#include<cstring>
#define mid ((l+r)>>1)
using namespace std;
const int maxn=1e5+10;
struct point{
	int x,y;
	point(){}
	point(int X,int Y):x(X),y(Y){};
	friend inline int cross(const point &a,const point &b){return a.x*b.y-a.y*b.x;}
	friend inline point operator-(const point &a,const point &b){return point(a.x-b.x,a.y-b.y);}
}now;
struct line{point p[2];}L[maxn];
int ans[maxn],A,B,n,m,a,b,c,d,p,q,l,r;
int main(){
	while(scanf("%d",&n)==1&&n){
		memset(ans,0,sizeof(ans));
		scanf("%d%d%d%d%d",&m,&a,&b,&c,&d);
		for(int i=0;i<n;++i)
		scanf("%d%d",&p,&q),L[i].p[0]=point(p,b),L[i].p[1]=point(q,d);
		//p[0]是上面的点，p[1]是下面的。 
		while(m--){
			scanf("%d%d",&p,&q),now=point(p,q),l=0,r=n;
			while(l<r){
				if(cross(now-L[mid].p[1],L[mid].p[0]-L[mid].p[1])>0) l=mid+1;
				else r=mid;
			}ans[l]++;
		}for(int i=0;i<=n;++i) printf("%d: %d\n",i,ans[i]);
		putchar(10);
	}
}