2015长春 HDU 5531 Rebuild

题意：n个顶点组成的多边形能否形成正多边形？

 #include <cstdio>
 #include <cstring>
 #include <cmath>
 #include <cstdlib>
 #include <iostream>
 #include <algorithm>
 #include <queue>
 #include <map>
 #include <vector>
 using namespace std;
 const int maxn=;
 const int maxnode=;
 typedef long long LL;
 struct Point
 {
     int x,y;
     Point (int x=,int y=):x(x),y(y) {}

 } p[maxn];
 typedef Point Vector;
 Vector operator+(Vector A,Vector B)
 {
     return Vector(A.x+B.x,A.y+B.y);
 }

 Vector operator-(Point A,Point B)
 {
     return Vector(A.x-B.x,A.y-B.y);
 }
 Vector operator*(Vector A,int p)
 {
     return Vector(A.x*p,A.y*p);
 }

 Vector operator /(Vector A,int p)
 {
     return Vector(A.x/p,A.y/p);
 }

 bool operator <(const Point&a,const Point &b)
 {
     return a.x<b.x||(a.x==b.x&&a.y<b.y);
 }

 int Cross(Vector A,Vector B)
 {
     return A.x*B.y-A.y*B.x;
 }

 int ConvexHull(Point *p,int n,Point *ch)
 {
     sort(p,p+n);
     int m=;
     for(int i=; i<n; i++)
     {
         while(m>&&Cross(ch[m-]-ch[m-],p[i]-ch[m-])<=)
             m--;
         ch[m++]=p[i];
     }
     int k=m;
     for(int i=n-; i>=; i--)
     {
         while(m>k&&Cross(ch[m-]-ch[m-],p[i]-ch[m-])<=)m--;
         ch[m++]=p[i];
     }
     if(n>)
         m--;
     return m;
 }
 int n;
 Point ans[maxn];
 LL  dis(LL X1,LL Y1,LL X2,LL Y2)
 {
     return (X1-X2)*(X1-X2)+(Y1-Y2)*(Y1-Y2);
 }
 int main()
 {
     freopen("in.txt","r",stdin);
     int t ;
     scanf("%d",&t);
     while(t--)
     {
         scanf("%d",&n);
         for(int i=; i<n; i++)
             scanf("%d%d",&p[i].x,&p[i].y);
         int m=ConvexHull(p,n,ans);
         if(m!=n)
         {
             printf("NO\n");
             continue;
         }
         bool flag=true;
         LL len=dis(ans[].x,ans[].y,ans[m-].x,ans[m-].y);

         for(int i=; i<m; i++)
         {
             if(len!=dis(ans[i].x,ans[i].y,ans[i-].x,ans[i-].y))
             {
                 flag=false;
                 break;
             }
         }
         if(flag)printf("YES\n");
         else printf("NO\n");

     }
     return ;
 }