[HDU 4082] Hou Yi's secret (简单计算几何)

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=4082

题目大意：

给你n个点，问能最多构成多少个相似三角形。

用余弦定理，计算三个角度，然后暴力数有多少个，更新答案。

代码：

 #include <cstdio>
 #include <cmath>
 #include <algorithm>
 #include <cstring>
 #include <vector>
 #include <set>
 using namespace std;
 typedef pair<int,int> PII;
 typedef long long LL;

 #define EPS 1e-8
 #define PB push_back

 struct POINT{
     int x,y;
     double dis(const POINT& b){
         return sqrt( double(x-b.x)*double(x-b.x)+double(y-b.y)*double(y-b.y) );
     }
     POINT(int ax=,int ay=):x(ax),y(ay){}
     bool operator==(const POINT &b) const{
         return x==b.x&&y==b.y;
     }
     bool operator<(const POINT &b) const{
         if( x==b.x ) return y<b.y;
         return x<b.x;
     }
 };

 struct triangle{
     double cosa[];
     triangle(){}

     triangle(POINT a,POINT b,POINT c){
         double A = a.dis(b);
         double B = a.dis(c);
         double C = b.dis(c);

         cosa[] = (A*A+B*B-C*C)/(*A*B);
         cosa[] = (B*B+C*C-A*A)/(*B*C);
         cosa[] = (A*A+C*C-B*B)/(*A*C);
         sort(cosa,cosa+);
     }

     triangle(double a,double b,double c){
         cosa[] = a;
         cosa[] = b;
         cosa[] = c;
         sort(cosa,cosa+);
     }

     bool operator==(const triangle& b) const{
         return fabs(cosa[]-b.cosa[])<EPS&&fabs(cosa[]-b.cosa[])<EPS&&fabs(cosa[]-b.cosa[])<EPS;
     }

 };

 bool isLine(POINT a,POINT b,POINT c){
     return (c.x-a.x)*(b.y-a.y) == (b.x-a.x)*(c.y-a.y);
 }

 POINT pt[];
 int n;

 int main(){
     while( scanf("%d",&n)!=EOF && n ){
         set<POINT> st;
         int ptrb = ;
         for(int i=;i<n;i++){
             int x,y;
             scanf("%d%d",&x,&y);
             if( st.find(POINT(x,y))==st.end() ){
                 pt[ptrb++] = POINT(x,y);
                 st.insert(POINT(x,y));
             }
         }

         vector<triangle> vec;
         for(int i=;i<ptrb;i++){
             for(int j=i+;j<ptrb;j++){
                 for(int k=j+;k<ptrb;k++){
                     if( !isLine(pt[i],pt[j],pt[k])){
                         vec.PB(triangle(pt[i],pt[j],pt[k]));
                     }
                 }
             }
         }

         int maxn = ;

         for(size_t i=;i<vec.size();i++){
             int as = ;

             for(size_t j=i+;j<vec.size();j++){
                 if( vec[i]==vec[j] ) as++;
             }
             maxn = max(as,maxn);
         }
         printf("%d\n",maxn);
     }
     return ;
 }