poj1971Parallelogram Counting

 1 #include <iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 #include<stdlib.h>
 6 #include<vector>
 7 #include<cmath>
 8 #include<queue>
 9 #include<set>
10 #include<map>
11 using namespace std;
12 #define N 1010
13 #define LL long long
14 #define INF 0xfffffff
15 const double eps = 1e-8;
16 const double pi = acos(-1.0);
17 const double inf = ~0u>>2;
18 struct point
19 {
20     int x,y;
21 } p[N],o[N*N];
22 
23 bool cmp(point a,point b)
24 {
25     if(a.x==b.x) return a.y<b.y;
26     return a.x<b.x;
27 }
28 int main()
29 {
30     int t,n,i,j;
31     cin>>t;
32     while(t--)
33     {
34         scanf("%d",&n);
35         for(i = 1 ; i <= n ; i++)
36         {
37             scanf("%d%d",&p[i].x,&p[i].y);
38         }
39         int g = 0;
40         for(i = 1 ; i<= n ; i++)
41         {
42             for(j = i+1 ; j <= n ;j++)
43             {
44                 o[++g].x = (p[i].x+p[j].x);
45                 o[g].y = (p[i].y+p[j].y);
46                // cout<<o[g].y<<endl;
47             }
48         }
49         LL ans = 0;
50         sort(o+1,o+g+1,cmp);
51         int e = 1;
52         for(i = 2; i <= g ;i++)
53         {
54             if(o[i].x-o[i-1].x==0&&o[i].y-o[i-1].y==0)
55             {
56                 e++;
57                // cout<<o[i].x<<" ,"<<o[i-1].x<<" "<<o[i].y<<" "<<o[i-1].y<<endl;
58             }
59             else
60             {
61                 ans+=(LL)(e-1)*e/2;
62                 e = 1;
63             }
64         }
65         ans+=(LL)(e-1)*e/2;
66         cout<<ans<<endl;
67     }
68     return 0;
69 }