POJ 2398 Toy Storage

题意：判断点是否在凸多边形内

#include <iostream>
#include <cstring>
#include <string>
#include <cmath>
#include <algorithm>
#include <cstdio>
using namespace std;
#define eps 1e-8
#define _sign(x) ((x)>eps?1:((x)<-eps?2:0))
struct point
{
    int x,y;
    point()
    {

    }
    point(int xx,int yy)
    {
        x=xx;
        y=yy;
    }
} p[2005],w[5],A,B;
struct node
{
    point a,b;
} d[2005];
bool cmp(node A,node B)
{
    return A.a.x<B.a.x;
}
double cross(point a,point b,point c)
{
    return (b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x);
}
int inside_convex(point q,int n)
{
    int i,s[3]= {1,1,1};
    for (i=0; i<n&&s[1]|s[2]; i++)
        s[_sign(cross(w[i],w[(i+1)%n],q))]=0;
    return s[1]|s[2];
}
void solve(int id)
{
    w[0]=d[id-1].a;
    w[1]=d[id-1].b;
    w[2]=d[id].b;
    w[3]=d[id].a;
}
int f[2005];
int t[2005];
int main()
{
    int T,i,j,k,m,n;
    while(scanf("%d",&n)!=EOF)
    {
        if(n==0) break;
        memset(t,0,sizeof(t));
        memset(f,0,sizeof(f));
        scanf("%d",&m);
        scanf("%d%d",&A.x,&A.y);
        scanf("%d%d",&B.x,&B.y);
        d[0].a=A;
        d[0].b=point(A.x,B.y);
        for(i=1; i<=n; i++)
        {
            scanf("%d%d",&d[i].a.x,&d[i].b.x);
            d[i].a.y=A.y;
            d[i].b.y=B.y;
        }
        d[i].a=point(B.x,A.y);
        d[i].b=B;
        n+=2;
        sort(d,d+n,cmp);
        for(i=0;i<m;i++)
            scanf("%d%d",&p[i].x,&p[i].y);
        for(i=1;i<n;i++)
        {
            solve(i);
            for(j=0;j<m;j++)
                if(inside_convex(p[j],4)) f[i]++;
        }
        for(i=0;i<2001;i++)
            t[f[i]]++;
        printf("Box\n");
        for(i=1;i<2001;i++)
            if(t[i]) printf("%d: %d\n",i,t[i]);
    }
}