POJ -- 2002

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<string>
 5 #include<algorithm>
 6 #define MAXN 1111
 7 using namespace std;
 8 class Point{
 9     public:
10         int x,y;
11         bool operator < (const Point &p) const{
12             if(x == p.x) return y < p.y;
13             return x < p.x;
14         }
15         bool operator == (const Point &p) const{
16             return x == p.x && y == p.y;
17         }
18 };
19 Point P[MAXN];
20 bool Binary_Search(const Point target,int len){
21     int l = 0,r = len,mid;
22     while(l <= r){
23         mid = (l+r) >> 1;
24         if(target == P[mid]) return true;
25         else if(target < P[mid]) r = mid-1;
26         else l = mid+1;
27     }
28     return false;
29 }
30 int main(){
31     int n,ans;
32     freopen("in.c","r",stdin);
33     while(~scanf("%d",&n) && n){
34         for(int i = 0;i < n;i ++) scanf("%d%d",&P[i].x,&P[i].y);
35         sort(P,P+n);
36         ans = 0;
37         for(int i = 0;i < n;i ++){
38             for(int j = i+1;j < n;j ++){
39                 Point tmp1,tmp2;
40                 tmp1.x = P[i].x+P[i].y-P[j].y,tmp1.y = P[i].y-P[i].x+P[j].x;
41                 tmp2.x = P[j].x+P[i].y-P[j].y,tmp2.y = P[j].y-P[i].x+P[j].x;
42                 if(Binary_Search(tmp1,n) && Binary_Search(tmp2,n)) ans++;
43             }
44         }
45         printf("%d
",ans >> 1);
46     }
47     return 0;
48 }