poj How I Mathematician Wonder What You Are! 求多边形的核

#include <iostream>
#include<cmath>
using namespace std;
const double EPS=1e-8;
const int MAXN=100;
struct point
{
    double x,y;
};
struct cp
{
    int n;
    point p[MAXN];
};
//求直线a1*x+b1*y+c1=0与a2*x+b2*y+c2=0的交点
point intersectL(double a1, double b1, double c1, double a2, double b2, double c2)
{
    point ret;
    ret.y = (a1 * c2 - c1 * a2) / (b1 * a2 - a1 * b2);
    if (fabs(a2) < EPS)
        ret.x = -(b1 * ret.y + c1) / a1;
    else
        ret.x = -(b2 * ret.y + c2) / a2;
    return ret;
}
//判断点inpa与点inpb是否相同
bool isEqual(point inpA, point inpB)
{
    return (fabs(inpA.x - inpB.x) < EPS && fabs(inpA.y - inpB.y) < EPS);
}
//求向量AB与向量AC的叉乘
double Cross(point inpA, point inpB, point inpC)
{
    return (inpB.x - inpA.x) * (inpC.y - inpA.y) - (inpC.x - inpA.x) * (inpB.y - inpA.y);
}
//求由点A，B构成的直线a*x+b*y+c=0；
void Get_line(point inpA, point inpB, double &a1, double &b1, double &c1)
{
    a1 = inpB.y - inpA.y;
    b1 = inpA.x - inpB.x;
    c1 = inpA.y * (inpB.x - inpA.x) - inpA.x * (inpB.y - inpA.y);
}

cp cut(point inpA, point inpB, cp incp)
{
    cp ret;
    point cross;
    int i, j;
    double t1, t2;
    double a1, b1, c1, a2, b2, c2;
    ret.n = 0;
    for (i = 0; i < incp.n; i++)
    {
        j = i + 1;
        t1 = Cross(inpA, inpB, incp.p[i]);
        t2 = Cross(inpA, inpB, incp.p[j]);
        if (t1 < EPS && t2 < EPS)
        {
            ret.p[ret.n++] = incp.p[i];
            ret.p[ret.n++] = incp.p[j];
        }
        else if (t1 > EPS && t2 > EPS)
            continue;
        else
        {
            Get_line(inpA, inpB, a1, b1, c1);
            Get_line(incp.p[i], incp.p[j], a2, b2, c2);
            cross = intersectL(a1, b1, c1, a2, b2, c2);
            if (t1 < EPS)
            {
                ret.p[ret.n++] = incp.p[i];
                ret.p[ret.n++] = cross;
            }
            else
            {
                ret.p[ret.n++] = cross;
                ret.p[ret.n++] = incp.p[j];
            }
        }
    }
    if (ret.n == 0)
        return ret;
    for (i = 1, j = 1; i < ret.n; i++)
        if (!isEqual(ret.p[i - 1], ret.p[i]))
            ret.p[j++] = ret.p[i];
    ret.n = j;
    if (ret.n != 1 && isEqual(ret.p[ret.n - 1], ret.p[0]))
        ret.n--;
    ret.p[ret.n] = ret.p[0];
    return ret;
}
int main()
{
   // freopen("input.txt","r",stdin);
   int n,i;
   cp input,ret;
   while(cin>>n&&n)
   {
       input.n=n;
       for(i=0;i<n;i++)
              cin>>input.p[n-i-1].x>>input.p[n-i-1].y;
        input.p[input.n]=input.p[0];
        ret=input;
        for(i=0;i<input.n;i++)
        {
            ret=cut(input.p[i],input.p[i+1],ret);
        }
        if(ret.n>=1)
        cout<<1<<endl;
        else cout<<0<<endl;
   }
    return 0;
}