[HDU 4082] Hou Yi's secret (简单计算几何)

  1 #include <cstdio>
  2 #include <cmath>
  3 #include <algorithm>
  4 #include <cstring>
  5 #include <vector>
  6 #include <set>
  7 using namespace std;
  8 typedef pair<int,int> PII;
  9 typedef long long LL;
 10 
 11 #define EPS 1e-8
 12 #define PB push_back
 13 
 14 struct POINT{
 15     int x,y;
 16     double dis(const POINT& b){
 17         return sqrt( double(x-b.x)*double(x-b.x)+double(y-b.y)*double(y-b.y) );
 18     }
 19     POINT(int ax=0,int ay=0):x(ax),y(ay){}
 20     bool operator==(const POINT &b) const{
 21         return x==b.x&&y==b.y;
 22     }
 23     bool operator<(const POINT &b) const{
 24         if( x==b.x ) return y<b.y;
 25         return x<b.x;
 26     }
 27 };
 28 
 29 struct triangle{
 30     double cosa[3];
 31     triangle(){}
 32 
 33     triangle(POINT a,POINT b,POINT c){
 34         double A = a.dis(b);
 35         double B = a.dis(c);
 36         double C = b.dis(c);
 37 
 38         cosa[0] = (A*A+B*B-C*C)/(2*A*B);
 39         cosa[1] = (B*B+C*C-A*A)/(2*B*C);
 40         cosa[2] = (A*A+C*C-B*B)/(2*A*C);
 41         sort(cosa,cosa+3);
 42     }
 43 
 44     triangle(double a,double b,double c){
 45         cosa[0] = a;
 46         cosa[1] = b;
 47         cosa[2] = c;
 48         sort(cosa,cosa+3);
 49     }
 50 
 51     bool operator==(const triangle& b) const{
 52         return fabs(cosa[0]-b.cosa[0])<EPS&&fabs(cosa[1]-b.cosa[1])<EPS&&fabs(cosa[2]-b.cosa[2])<EPS;
 53     }
 54 
 55 };
 56 
 57 bool isLine(POINT a,POINT b,POINT c){
 58     return (c.x-a.x)*(b.y-a.y) == (b.x-a.x)*(c.y-a.y);
 59 }
 60 
 61 POINT pt[20];
 62 int n;
 63 
 64 int main(){
 65     while( scanf("%d",&n)!=EOF && n ){
 66         set<POINT> st;
 67         int ptrb = 0;
 68         for(int i=0;i<n;i++){
 69             int x,y;
 70             scanf("%d%d",&x,&y);
 71             if( st.find(POINT(x,y))==st.end() ){
 72                 pt[ptrb++] = POINT(x,y);
 73                 st.insert(POINT(x,y));
 74             }
 75         }
 76 
 77 
 78         vector<triangle> vec;
 79         for(int i=0;i<ptrb;i++){
 80             for(int j=i+1;j<ptrb;j++){
 81                 for(int k=j+1;k<ptrb;k++){
 82                     if( !isLine(pt[i],pt[j],pt[k])){
 83                         vec.PB(triangle(pt[i],pt[j],pt[k]));
 84                     }
 85                 }
 86             }
 87         }
 88 
 89         int maxn = 0;
 90 
 91         for(size_t i=0;i<vec.size();i++){
 92             int as = 1;
 93 
 94             for(size_t j=i+1;j<vec.size();j++){
 95                 if( vec[i]==vec[j] ) as++;
 96             }
 97             maxn = max(as,maxn);
 98         }
 99         printf("%d\n",maxn);
100     }
101     return 0;
102 }