poj2002Squares(点集组成正方形数）

 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 using namespace std;
11 #define N 1010
12 #define mod 99991
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     point(int x=0,int y=0):x(x),y(y){}
22 }p[N],o[N];
23 int next[N],head[mod],t;
24 void insert(int i)
25 {
26     int key = (p[i].x*p[i].x+p[i].y*p[i].y)%mod;
27     next[t] = head[key];
28     o[t].x = p[i].x;
29     o[t].y = p[i].y;
30     head[key] = t++;
31 }
32 int find(point a)
33 {
34     int  key = (a.x*a.x+a.y*a.y)%mod;
35     int i;
36     for(i = head[key] ; i!= -1 ; i = next[i])
37     {
38         if(o[i].x==a.x&&o[i].y == a.y) return 1;
39     }
40     return 0;
41 }
42 bool cmp(point a,point b)
43 {
44     if(a.x==b.x)
45     return a.y<b.y;
46     return a.x<b.x;
47 }
48 int main()
49 {
50     int n,i,j;
51     while(scanf("%d",&n)&&n)
52     {
53         memset(head,-1,sizeof(head));
54         t = 0;
55         for(i = 1; i <= n; i++)
56         {
57             scanf("%d%d",&p[i].x,&p[i].y);
58             insert(i);
59         }
60         //sort(p+1,p+n+1,cmp);
61         int ans = 0;
62         for(i = 1; i <= n ;i++)
63             for(j = 1 ; j <= n; j++)
64             {
65                 if(i==j) continue;
66                 point p1,p2;
67                 p1.x = p[i].x+(p[i].y-p[j].y);
68                 p1.y = p[i].y-(p[i].x-p[j].x);
69                 p2.x = p[j].x+(p[i].y-p[j].y);
70                 p2.y = p[j].y-(p[i].x-p[j].x);
71                 if(!find(p1)) continue;
72                 if(!find(p2)) continue;
73                 ans++;
74             }
75         printf("%d\n",ans/4);
76     }
77     return 0;