题目传送门
1 /*
2 好吧，我不是地球人，这题只要判断正方形就行了，正三角形和正五边形和正六边形都不可能(点是整数)。
3 但是，如果不是整数，那么该怎么做呢？是否就此开启计算几何专题了呢
4 */
5 /************************************************
6 * Author :Running_Time
7 * Created Time :2015-8-8 19:54:14
8 * File Name :B.cpp
9 ************************************************/
10
11 #include <cstdio>
12 #include <algorithm>
13 #include <iostream>
14 #include <sstream>
15 #include <cstring>
16 #include <cmath>
17 #include <string>
18 #include <vector>
19 #include <queue>
20 #include <deque>
21 #include <stack>
22 #include <list>
23 #include <map>
24 #include <set>
25 #include <bitset>
26 #include <cstdlib>
27 #include <ctime>
28 using namespace std;
29
30 #define lson l, mid, rt << 1
31 #define rson mid + 1, r, rt << 1 | 1
32 typedef long long ll;
33 const int MAXN = 22;
34 const int INF = 0x3f3f3f3f;
35 const int MOD = 1e9 + 7;
36 struct Point {
37 int x, y;
38 }p[MAXN];
39 int id[10];
40 int n, tot;
41
42 int cal_dis(int x1, int y1, int x2, int y2) {
43 return (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
44 }
45
46 bool judge(void) {
47 int tt = 0; int d[20];
48 for (int i=1; i<=4; ++i) {
49 for (int j=i+1; j<=4; ++j) {
50 d[++tt] = cal_dis (p[id[i]].x, p[id[i]].y, p[id[j]].x, p[id[j]].y);
51 }
52 }
53 sort (d+1, d+1+tt);
54 for (int i=1; i<=3; ++i) if (d[i] != d[i+1]) return false;
55 if (d[5] != d[6]) return false;
56 if (d[5] != d[1] * 2) return false;
57 return true;
58 }
59
60 void DFS(int s, int num) {
61 if (num == 4) {
62 if (judge ()) tot++;
63 return ;
64 }
65 for (int i=s+1; i<=n; ++i) {
66 id[num+1] = i;
67 DFS (i, num + 1);
68 }
69 }
70
71 void work(void) {
72 tot = 0;
73 DFS (0, 0);
74 printf ("%d
", tot);
75 }
76
77 int main(void) { //BestCoder Round #50 (div.2) 1002 Run
78 while (scanf ("%d", &n) == 1) {
79 for (int i=1; i<=n; ++i) {
80 scanf ("%d%d", &p[i].x, &p[i].y);
81 }
82 if (n < 3) {
83 puts ("0"); continue;
84 }
85 work ();
86 }
87
88 return 0;
89 }