UVA - 1595 Symmetry

#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;
#define inf (0x3f3f3f3f)
typedef long long int LL;

#include <iostream>
#include <sstream>
#include <vector>
#include <set>
#include <map>
#include <queue>
#include <string>
const double eps = 1e-7;
bool same (double a,double b)
{
    return fabs(a-b)<eps;
}
struct coor
{
    int x,y;
    coor(){}
    coor(int xx,int yy):x(xx),y(yy){}
    double operator ^(coor rhs) const //计算叉积（向量积），返回数值即可
    {
        return x*rhs.y - y*rhs.x;
    }
    coor operator -(coor rhs) const //坐标相减，a-b得到向量ba，返回一个向量（坐标形式）
    {
        return coor(x-rhs.x,y-rhs.y);
    }
    double operator *(coor rhs) const //数量积，返回数值即可
    {
        return x*rhs.x + y*rhs.y;
    }
    bool operator ==(coor rhs) const
    {
        return same(x,rhs.x)&&same(y,rhs.y); //same的定义其实就是和eps比较
    }
    bool operator < (coor rhs) const
    {
        if (x!=rhs.x) return x<rhs.x;
        else return y<rhs.y;
    }
};   //记得这里有个分号
set<struct coor>ss;
void work ()
{
    ss.clear();
    int n;
    cin>>n;
    for (int i=1;i<=n;++i)
    {
        int x,y;
        scanf("%d%d",&x,&y);
        x*=2; y*=2;
        ss.insert(coor(x,y));
    }
    int bx;
    set<struct coor>::iterator it = ss.begin();
    //printf ("%d %d\n",it->x,it->y);
    bx = it->x;
    while (it!=ss.end()) ++it;
    it--;
    bx += it->x;
    bx/=2;

    int now_calc = 0;
    for (it=ss.begin();it!=ss.end() && 2*now_calc <= n;it++)
    {
        int tx = 2*bx - it->x;
        int ty = it->y;
        if (ss.find(coor(tx,ty))==ss.end())
        {
            printf ("NO\n");
            return ;
        }
        now_calc++;
    }
    printf ("YES\n");
    return ;
}
int main()
{
#ifdef local
    freopen("data.txt","r",stdin);
#endif
    int t;
    cin>>t;
    while (t--)
        work();
    return 0;
}