HDU 5365 Run

Description

有N个格点，取若干个点组成正多边形，问有几个

Algorithm

格点正方形只有正方形
枚举4个点
然后就是这题算法

Code

#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 20 + 9;
struct P
{
  int x, y;
};
int dist2(P a, P b)
{
  return (a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y);
}
bool ok(P a, P b, P c, P dd)
{
  int d[6];
  d[0] = dist2(a, b);
  d[1] = dist2(a, c);
  d[2] = dist2(a, dd);
  d[3] = dist2(b, c);
  d[4] = dist2(b, dd);
  d[5] = dist2(c, dd);
  sort(d, d + 6);
  if (d[0] == d[1] && d[1] == d[2] && d[2] == d[3] && d[4] == d[5] && d[3] * 2 == d[4]) return true;
  return false;
}
int main()
{
  int n;
  while (cin >> n)
  {
    P a[maxn];
    for (int i = 0; i < n; i++)
      cin >> a[i].x >> a[i].y;
    int ans = 0;
    for (int i = 0; i < n; i++)
      for (int j = 0;j < i; j++)
        for (int k = 0; k < j;k++)
          for (int kk = 0; kk < k; kk++)
            if (ok(a[i], a[j], a[k], a[kk]))
              ans++;
    cout << ans << endl;
  }
}