fzu 2148 Moon Game(计算几何)

http://acm.fzu.edu.cn/contest/problem.php?cid=134&sortid=9

#include<cstdio>
#include<cmath>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;
struct Node
{
  double x,y;
};
Node node[50];
double xmult(double x0,double y0,double x1,double y1,double x2,double y2)
{
  return (x1-x0)*(y2-y0)-(x2-x0)*(y1-y0);
}
double ss(double x1,double y1,double x2,double y2,double x3,double y3)
{
  return fabs(xmult(x1,y1,x2,y2,x3,y3))/2;
}
int main()
{
  int t,n;
  int i,j,k,l;
  int cas=1;
  scanf("%d",&t);
  while(t--)
  {
    int ans=0;
    scanf("%d",&n);
    for(i=0;i<n;i++)
    {
      scanf("%lf%lf",&node[i].x,&node[i].y);
    }
    if(n<=3)
    {
      printf("Case %d: 0
",cas++);
      continue;
    }
    for(i=0;i<n-3;i++)
    {
      for(j=i+1;j<n-2;j++)
      {
        for(k=j+1;k<n-1;k++)
        {
          for(l=k+1;l<n;l++)
          {
            double s1=ss(node[i].x,node[i].y,node[j].x,node[j].y,node[k].x,node[k].y);
            double s2=ss(node[i].x,node[i].y,node[j].x,node[j].y,node[l].x,node[l].y);
            double s3=ss(node[l].x,node[l].y,node[j].x,node[j].y,node[k].x,node[k].y);
            double s4=ss(node[i].x,node[i].y,node[l].x,node[l].y,node[k].x,node[k].y);
            if(s1+s2+s3!=s4&&s1+s2+s4!=s3&&s1+s3+s4!=s2&&s2+s3+s4!=s1) ans++;
          }
        }
      }
    }
    printf("Case %d: ",cas++);
    printf("%d
",ans);
  }
  return 0;
}