POJ 2318 判定点在多边形内外（二分）

题意：图片是一个俯视图，按照从左到右的顺序输入边 然后输入点坐标，问从左到右的各个区域分别有多少玩具。

已知顺序只需要二分来确定区间，然后得出结果。

#include <iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
struct point
{
    double x,y;
};
struct edge
{
    point up,down;
};
double Direction(point a,point b,point c)
{
    return (b.x-a.x)*(c.y-a.y)-(c.x-a.x)*(b.y-a.y);
}
bool On_Segment(point pi,point pj,point pk)
{
    if(pk.x>=min(pi.x,pj.x)&&pk.x<=max(pi.x,pj.x)&&pk.y>=min(pi.y,pj.y)&&pk.y<=max(pi.y,pj.y))
        return 1;
    return 0;
}
bool Segment_Intersect(point p1,point p2,point p3,point p4)
{
    double d1=Direction(p3,p4,p1),d2=Direction(p3,p4,p2),d3=Direction(p1,p2,p3),d4=Direction(p1,p2,p4);
    if(((d1>0&&d2<0)||(d1<0&&d2>0))&&((d3>0&&d4<0)||(d3<0&&d4>0)))
        return 1;
    if(d1==0&&On_Segment(p3,p4,p1))
        return 1;
    if(d2==0&&On_Segment(p3,p4,p2))
        return 1;
    if(d3==0&&On_Segment(p1,p2,p3))
        return 1;
    if(d4==0&&On_Segment(p1,p2,p4))
        return 1;
    return 0;
}
int Pandingdian(point a,edge l,edge r)//1在多边形上 2在多边形外 0在多边形内
{
    point b,polygon[6];
    b.x=-9999999,b.y=a.y;
    int n=4,sum=0;
    polygon[0]=l.up,polygon[1]=l.down,polygon[2]=r.down,polygon[3]=r.up;
    polygon[n]=polygon[0];
    for(int i=1; i<=n; i++)
        if(polygon[i].y-polygon[i-1].y!=0&&Segment_Intersect(a,b,polygon[i],polygon[i-1]))
        {
            if(Direction(a,polygon[i],polygon[i-1])==0)
                return 1;
            sum++;
        }
    if(sum&1)
        return 0;
    return 2;
}
point lt,rb,temp;
edge data[5005];
int main()
{
    int n,m,ans[5005],s=0;
    while(~scanf("%d",&n),n)
    {
        scanf("%d%lf%lf%lf%lf",&m,<.x,<.y,&rb.x,&rb.y);
        if(s)
            printf("\n");
        s++;
        memset(ans,0,sizeof(ans));
        data[0].up=lt,data[0].down.x=lt.x,data[0].down.y=rb.y;
        point u,d;
        u.y=lt.y,d.y=rb.y;
        for(int i=1; i<=n; i++)
            scanf("%lf%lf",&u.x,&d.x),data[i].up=u,data[i].down=d;
        data[n+1].down=rb,data[n+1].up.y=lt.y,data[n+1].up.x=rb.x;
        while(m--)
        {
            scanf("%lf%lf",&temp.x,&temp.y);
            int l=0,r=n+1,mid;
            while(l<r)
            {
                mid=(l+r)/2;
                int w=Pandingdian(temp,data[mid],data[r]);
                if(w==0||w==1)
                {
                    if(r-mid==1)
                    {
                        ans[mid]++;
                        break;
                    }
                    l=mid;
                }
                else if(mid-l==1)
                {
                    ans[l]++;
                    break;
                }
                else
                    r=mid;
            }
        }
        for(int i=0; i<=n; i++)
            printf("%d: %d\n",i,ans[i]);
    }
    return 0;
}