POJ 1971 Parallelogram Counting

#include<iostream>
#include<string>
#include<cstring>
#include<cmath>
#include<cstdio>

const long long maxsize = 0x1fffff;
const int maxn = 1010;

using namespace std;

struct Point{
int x,y;
}p[maxn],mid[maxn*maxn];

int head[maxsize],next[maxn*maxn];

void init_hash(){
memset(head,-1,sizeof(head));
}

int get_hash(Point p){
return ((long long)p.x+p.y)&maxsize;
}

int insert(int i){
int h=get_hash(mid[i]);
//cout<<h<<endl;
int res=0;
int u=head[h];
while(u!=-1){
if(mid[u].x==mid[i].x&&mid[u].y==mid[i].y)
res++;
u=next[u];
}
next[i]=head[h];
head[h]=i;
return res;
}

int main()
{
int t;
cin>>t;
while(t--){
int n,i,ans=0,j;
cin>>n;
for(i=0;i<n;i++)
cin>>p[i].x>>p[i].y;
int cnt=0;
for(i=0;i<n;i++)
for(j=i+1;j<n;j++){
mid[cnt].x=p[i].x+p[j].x;
mid[cnt++].y=p[i].y+p[j].y;
}
init_hash();
for(i=0;i<cnt;i++)
ans+=insert(i);
cout<<ans<<endl;
}
return 0;
}

#include<iostream>
#include<string>
#include<cstring>
#include<cmath>
#include<cstdio>

const long long maxsize = 0x1fffff;
const int maxn = 1010;

using namespace std;

struct Point{
int x,y;
}p[maxn],mid[maxn*maxn];

int head[maxsize],next[maxn*maxn],res[maxn*maxn];

void init(){
memset(res,0,sizeof(res));
memset(head,-1,sizeof(head));
}

int get_hash(Point p){
return (((p.x<<2)+p.x>>4)^(p.y<<10))&maxsize;//传说这叫折叠法构造hash函数。。。
}

int insert(int i){
int h=get_hash(mid[i]);
//cout<<h<<endl;
int u=head[h];
while(u!=-1){
if(mid[u].x==mid[i].x&&mid[u].y==mid[i].y){
return res[u]++;
}
u=next[u];
}
next[i]=head[h];
head[h]=i;
res[i]=1;
return 0;
}

int main()
{
int t;
cin>>t;
while(t--){
int n,i,ans=0,j;
cin>>n;
for(i=0;i<n;i++)
cin>>p[i].x>>p[i].y;
int cnt=0;
for(i=0;i<n;i++)
for(j=i+1;j<n;j++){
mid[cnt].x=p[i].x+p[j].x;
mid[cnt++].y=p[i].y+p[j].y;
}
init();
for(i=0;i<cnt;i++)
ans+=insert(i);
cout<<ans<<endl;
}
return 0;
}