> 代码：
> #include <iostream>
> #include <string>
> #include <memory>
> #include <algorithm>
> using namespace std;
> 
> const int maxn = 1000;
> 
> struct node {
>     int x, y;
> }list[maxn];
> int n;
> 
> bool operator<(const node &a, const node &b)
> {
>     return (a.x < b.x || (a.x == b.x && a.y < b.y));
> }
> 
> bool init()
> {
>     cin >> n;
>     if (!n) return false;
>     int i;
>     for (i = 0; i < n; ++i) {
> 	cin >> list[i].x >> list[i].y;
> 	list[i].x *= 2;
> 	list[i].y *= 2;
>     }
>     sort(list, list + n);
>     return true;
> }
> 
> void run()
> {
>     int tot = 0;
>     int i, j;
>     int a, b;
>     int x, y;
>     node t1, t2;
>     for (i = 0; i < n; ++i) {
> 	for (j = i + 1; j < n; ++j) {
> 	    a = list[j].x - list[i].x;
> 	    b = list[j].y - list[i].y;
> 	    a /= 2;
> 	    b /= 2;
> 	    x = list[i].x + a;
> 	    y = list[i].y + b;
> 	    t1.x = x - b;
> 	    t1.y = y + a;
> 	    t2.x = x + b;
> 	    t2.y = y - a;
> 	    if (binary_search(list, list + n, t1) && binary_search(list, list + n, t2)) {
> 		++tot;
> 	    }
> 	}
>     }
>     cout << tot / 2 << endl;
> }
> 
> int main(void)
> {
>     while (init()) {
> 	run();
>     }
>     return 0;
> }
> 
>