codeforce 660D Number of Parallelograms

题意：询问多少个矩形。

统计横纵坐标差，放进vector中

 #include<cstdio>
 #include<cstring>
 #include<iostream>
 #include<queue>
 #include<stack>
 #include<bits/stdc++.h>
 using namespace std;
 #define LL long long
 int x[],y[];
 vector<pair<int,int> >v;
 int main(){
     int n;
     while(~scanf("%d",&n)){
        for(int i=;i<n;i++)
         scanf("%d%d",&x[i],&y[i]);

        for(int i=;i<n;i++){
         for(int j=i+;j<n;j++){
             //cout<<"~~"<<endl;
             int dx=x[i]-x[j];
             int dy=y[i]-y[j];
             if(dx<||(dx==&&dy<)){
                 dx=-dx,dy=-dy;
             }
             v.push_back(make_pair(dx,dy));
         }
        }
        //cout<<"~~"<<endl;
        sort(v.begin(),v.end());
        //printf("size:%d\n",v.size());
        LL cnt=;
        LL ans=;
        for(int i=;i<(int)v.size()-;i++){
            cnt++;
            if(v[i+]!=v[i]){
              ans+=cnt*(cnt-)/;
              cnt=;
            }
         }
         printf("%I64d\n", ans/);
     }
     return ;
 }