poj1859The Perfect Symmetry

链接

按x或y排序，假如有对称点的话，头尾相对。

 #include <iostream>
 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<stdlib.h>
 #include<vector>
 #include<cmath>
 #include<queue>
 #include<set>
 using namespace std;
 #define N 100000
 #define LL long long
 #define INF 0xfffffff
 const double eps = 1e-;
 const double pi = acos(-1.0);
 const double inf = ~0u>>;
 struct Point
 {
     double x,y;
     Point(double x=,double y=):x(x),y(y) {}
 }p[N];
 typedef Point pointt;
 pointt operator + (Point a,Point b)
 {
     return Point(a.x+b.x,a.y+b.y);
 }
 pointt operator - (Point a,Point b)
 {
     return Point(a.x-b.x,a.y-b.y);
 }
 int dcmp(double x)
 {
     if(fabs(x)<eps) return ;
     else return x<?-:;
 }
 bool cmp(Point a,Point b)
 {
     if(dcmp(a.x-b.x)==)
     return a.y<b.y;
     return a.x<b.x;
 }
 int main()
 {
     int n,i,j;
     while(scanf("%d",&n)&&n)
     {
         for(i = ; i <= n ;i++)
         scanf("%lf%lf",&p[i].x,&p[i].y);
         sort(p+,p+n+,cmp);
         double tx = (p[].x+p[n].x)/,ty = (p[].y+p[n].y)/;
         int flag = ;
         for(i =  ; i <= n; i++)
         {
             double x = (p[i].x+p[n-i+].x)/;
             double y = (p[i].y+p[n-i+].y)/;
             if(dcmp(x-tx)!=||dcmp(y-ty)!=)
             {
                 flag = ;
                 break;
             }
         }
         if(flag)
         printf("V.I.P. should stay at (%.1f,%.1f).\n",tx,ty);
         else
         printf("This is a dangerous situation!\n");
     }
     return ;
 }