【2017多校训练2+计算几何+板】HDU 6055 Regular polygon

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <algorithm>
 4 #include <cmath>
 5 #include<iostream>
 6 #include <vector>
 7 using namespace std ;
 8 #define eqs 1e-9
 9 struct node
10 {
11     double x , y ;
12 } p[1100] ;
13 bool cmp(node a,node b)
14 {
15     return ( a.x < b.x || ( a.x == b.x && a.y < b.y ) ) ;
16 }
17 bool judge(double x,double y,int n)
18 {
19     int low = 0 , mid , high = n-1 ;
20     while( low <= high )
21     {
22         mid = (low + high) / 2 ;
23         if( fabs(p[mid].x-x) < eqs && fabs(p[mid].y-y) < eqs )
24             return true ;
25         else if( p[mid].x-x > eqs || ( fabs(p[mid].x-x) < eqs && p[mid].y-y > eqs ) )
26             high = mid - 1 ;
27         else
28             low = mid + 1 ;
29     }
30     return false ;
31 }
32 int main()
33 {
34     int n,num;
35     double x,xx,y,yy;
36     while(scanf("%d", &n)!=EOF&&n)
37     {
38         num = 0 ;
39         for(int i = 0 ; i < n ; i++)
40         {
41             cin>>p[i].x>>p[i].y;
42         }
43         sort(p,p+n,cmp) ;
44         for(int i = 0 ; i < n ; i++)
45         {
46             for(int j = i+1 ; j < n ; j++)
47             {
48                 if( i == j ) continue ;
49                 x = (p[i].x+p[j].x)/2 ;
50                 y = (p[i].y+p[j].y)/2 ;
51                 xx = p[i].x - x ;
52                 yy = p[i].y - y ;
53                 if( judge(x+yy,y-xx,n) && judge(x-yy,y+xx,n) )
54                 {
55                     num++ ;
56                 }
57             }
58         }
59         cout<<num/2<<endl;
60     }
61     return 0;
62 }