【计算几何】【斜率】bzoj1610 [Usaco2008 Feb]Line连线游戏

枚举直线，计算斜率，排序，统计答案。

#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;
#define EPS 0.00000001
#define INF 99999999999999999999.0
#define N 201
typedef double db;
int n,m,sta,ans;
db xs[N],ys[N],line[N*N];
int main()
{
	scanf("%d",&n);
	for(int i=1;i<=n;++i)
	  scanf("%lf%lf",&xs[i],&ys[i]);
	for(int i=1;i<=n;++i)
	  for(int j=i+1;j<=n;++j)
	    line[++m]=(fabs(xs[i]-xs[j])<EPS?INF:(ys[i]-ys[j])/(xs[i]-xs[j]));
	sort(line+1,line+m+1);
	for(int i=1;i<=m;++i)
	  if(i==1||fabs(line[i]-line[i-1])>EPS)
	    ++ans;
	printf("%d\n",ans);
	return 0;
}