poj 1584

比较水的题，但是要细心，把情况考虑清楚

#include <cstdio>
#include <algorithm>
#include <cmath>
using namespace std;
const int maxn=10000;
const double eps=1e-8;
int n,f[maxn];
double rad;
struct Point
{
	double x,y;
};
Point ver[maxn],pel;
double cross(Point a,Point b,Point c,Point d)
{
	return (b.x-a.x)*(d.y-c.y)-(b.y-a.y)*(d.x-c.x);
}
double dis(Point a,Point b)
{
	return sqrt((b.x-a.x)*(b.x-a.x)+(b.y-a.y)*(b.y-a.y));
}
double getD(Point a,Point b,Point c)
{
	return fabs(cross(a,b,a,c))/dis(a,b);
}
int main()
{
	while(scanf("%d",&n)&&n>=3)
	{
		scanf("%lf%lf%lf",&rad,&pel.x,&pel.y);
		int i;
		for(i=0;i<n;i++)
			scanf("%lf%lf",&ver[i].x,&ver[i].y);
		ver[n].x=ver[0].x;ver[n].y=ver[0].y;
		int flag=1;
		for(i=2;i<=n;i++)
		{
			double tem=cross(ver[i-2],ver[i-1],ver[i-1],ver[i]);
			if(fabs(tem)<eps) f[i]=0;
			else if(tem<0) f[i]=-1;
			else f[i]=1;
		}
		int ju=0;
		for(i=3;i<=n;i++)
		{
			if(f[i]*f[i-1]<0)
			{
				flag=0;
				break;
			}
			else 
			{
				if(f[i]!=0) ju=f[i];
			}
		}
		if(!flag) printf("HOLE IS ILL-FORMED\n");
		else
		{
			flag=1;
			int flag2=1;
			if(ju==1)
			{
			for(i=0;i<n;i++)
			{
				if(cross(ver[i],ver[i+1],ver[i],pel)<eps)
				{
					flag=0;
					break;
				}
			}
			}
			else if(ju==-1)
			{
				for(i=0;i<n;i++)
				{
				if(cross(ver[i],ver[i+1],ver[i],pel)>-eps)
				{
					flag=0;
					break;
				}
			}
			}
			else flag=0;
			if(flag)
			{
				for(i=0;i<n;i++)
				{
					if(getD(ver[i],ver[i+1],pel)-rad<=-eps)
					{
						flag2=0;
						break;
					}
				}
			}
			if(flag&&flag2) printf("PEG WILL FIT\n");
			else printf("PEG WILL NOT FIT\n");
		}
	}
	return 0;
}