不过我用了STL里面的一些东西，感觉也不会超时啊。不甘心，我吧代码贴上来。。。
差不多就是HASH + 二分。。。难道是由于STL才超时。。。
#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

const int N = 100;
typedef struct
{
	int x, y;
}Point;
Point points[1000];
bool flag[N];
vector <int> hash[N];
int n;

bool check( int x1, int y1, int x2, int y2 )
{
	if( binary_search( hash[abs( x1 ) % N].begin(), hash[abs( x1 ) % N].end(), y1 ) == false )
		return false;
	if( binary_search( hash[abs( x2 ) % N].begin(), hash[abs( x2 ) % N].end(), y2 ) == false )
		return false;
	return true;
}

int main ()
{
	int i, j, count, x1, y1, x2, y2, test;

//	freopen ("1001.txt", "r", stdin);
	scanf( "%d", &test );
	while( test-- )
	{
		memset( flag, false, sizeof( flag ) );
		scanf( "%d", &n );
		count = 0;
		for ( i = 0; i < n; i++ ) //下面取模其实是HASH一个点
		{
			scanf ( "%d%d", &points[i].x, &points[i].y );
			int node = abs( points[i].x ) % N;
			hash[node].push_back( points[i].y );
			flag[node] = true;
		}

		for( i = 0; i < N; i++ )
			if( flag[i] )
				sort( hash[i].begin(), hash[i].end() );

		for ( i = 0; i < n; i++ )
			for ( j = i + 1; j < n; j++ )
			{
				x1 = points[i].x;
				y1 = points[i].y;
				x2 = points[j].x;
				y2 = points[j].y;

				if ( (x1 + x2 + y1 - y2 ) % 2 != 0 )
					continue;
				if ( (y1 + y2 + x2 - x1 ) % 2 != 0 )
					continue;
				if ( (x1 + x2 - y1 + y2 ) % 2 != 0 )
					continue;
				if ( (y1 + y2 + x1 - x2 ) % 2 != 0 )
					continue;

				int x3 = ( x1 + x2 + y1 - y2 ) / 2;
				int y3 = ( y1 + y2 + x2 - x1 ) / 2;
				int x4 = ( x1 + x2 - y1 + y2 ) / 2;
				int y4 = ( y1 + y2 + x1 - x2 ) / 2;

				if( x3 != x1 && x3 != x2 )
					continue;
				if( x4 != x1 && x4 != x2 )
					continue;
				if( y3 != y1 && y3 != y2 )
					continue;
				if( y4 != y1 && y4 != y2 )
					continue;

				if ( check ( x3, y3, x4, y4 ) )
					count++;
			}

	    printf ("%d\n", count / 2);

		for ( i = 0; i < N; i++ )
			if( flag[i] )
				hash[i].clear();
	}

	return 0;
}

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