poj2002 数正方形 hash

#include <iostream>
using namespace std;
struct gtype {
int x,y,next;
}g[3000];
int first[1000100],tot,n,x[3010],y[3010],ans,h,tx,ty;
int hash(int x,int y) {
return (40000*x+y+800040000)%999991+1;
}
bool find(int x,int y) {
int h = hash(x,y);
bool f = false;
for (int t=first[h];t!=-1;t=g[t].next)
if (g[t].x==x && g[t].y==y) {
f = true;
break;
}
return f;
}
int main() {
while (~scanf("%d",&n)) {
tot = 0;
memset(first,-1,sizeof(first));
for (int i=1;i<=n;i++) {
scanf("%d%d",&x[i],&y[i]);
h = hash(x[i],y[i]);
tot++;
g[tot].x = x[i];
g[tot].y = y[i];
g[tot].next = first[h];
first[h] = tot;
}
ans = 0;
for (int i=1;i<=n;i++)
for (int j=i+1;j<=n;j++) {
if (i==j) continue;
tx = x[i]-x[j];
ty = y[i]-y[j];
if (find(x[i]+ty,y[i]-tx) && find(x[j]+ty,y[j]-tx)) ans++;
if (find(x[i]-ty,y[i]+tx) && find(x[j]-ty,y[j]+tx)) ans++;
}
printf("%d\n",ans/4);
}
return 0;
}