POJ -- 2002

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<string>
 #include<algorithm>
 #define MAXN 1111
 using namespace std;
 class Point{
     public:
         int x,y;
         bool operator < (const Point &p) const{
             if(x == p.x) return y < p.y;
             return x < p.x;
         }
         bool operator == (const Point &p) const{
             return x == p.x && y == p.y;
         }
 };
 Point P[MAXN];
 bool Binary_Search(const Point target,int len){
     int l = ,r = len,mid;
     while(l <= r){
         mid = (l+r) >> ;
         if(target == P[mid]) return true;
         else if(target < P[mid]) r = mid-;
         else l = mid+;
     }
     return false;
 }
 int main(){
     int n,ans;
     freopen("in.c","r",stdin);
     while(~scanf("%d",&n) && n){
         for(int i = ;i < n;i ++) scanf("%d%d",&P[i].x,&P[i].y);
         sort(P,P+n);
         ans = ;
         for(int i = ;i < n;i ++){
             for(int j = i+;j < n;j ++){
                 Point tmp1,tmp2;
                 tmp1.x = P[i].x+P[i].y-P[j].y,tmp1.y = P[i].y-P[i].x+P[j].x;
                 tmp2.x = P[j].x+P[i].y-P[j].y,tmp2.y = P[j].y-P[i].x+P[j].x;
                 if(Binary_Search(tmp1,n) && Binary_Search(tmp2,n)) ans++;
             }
         }
         printf("%d\n",ans >> );
     }
     return ;
 }