POJ 2318 TOYS 叉积

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;

const int maxn=5000+5;
int cnt[maxn];

struct Point
{
    int x,y;
    Point() {};
    Point(int xx,int yy)
    {
        x=xx;
        y=yy;
    }
} Up[maxn],Lp[maxn],toys[maxn];

int crs_prdct(Point a,Point b)
{
    return a.x*b.y-b.x*a.y;
}

Point vct(Point a,Point b)
{
    return Point(a.x-b.x,a.y-b.y);
}

int main()
{
//    freopen("in.txt","r",stdin);
    int n,m,x1,y1,x2,y2;
    while(scanf("%d",&n),n)
    {
        memset(cnt,0,sizeof(cnt));
        scanf("%d",&m);
        scanf("%d%d",&x1,&y1);
        scanf("%d%d",&x2,&y2);
        Up[0]=Point(x1,y1);
        Up[n+1]=Point(x2,y1);
        Lp[0]=Point(x1,y2);
        Lp[n+1]=Point(x2,y2);
        for(int i=1; i<=n; i++)
        {
            int Ui,Li;
            scanf("%d%d",&Ui,&Li);
            Up[i]=Point(Ui,y1);
            Lp[i]=Point(Li,y2);
        }
        for(int i=0; i<m; i++)
            scanf("%d%d",&toys[i].x,&toys[i].y);
        for(int i=0; i<m; i++)
        {
            Point vct1,vct2,vct3,vct4;
            for(int j=0;j<=n; j++)
            {
                vct1=vct(Lp[j],toys[i]);
                vct2=vct(Up[j],toys[i]);
                vct3=vct(Lp[j+1],toys[i]);
                vct4=vct(Up[j+1],toys[i]);
                if(crs_prdct(vct1,vct2)<0 && crs_prdct(vct3,vct4)>0)
                {
                    cnt[j]++;
                    break;
                }
            }
        }
        for(int i=0;i<=n;i++)
            printf("%d: %d\n",i,cnt[i]);
        puts("");
    }
    return 0;
}