Squares<哈希>

Description

A square is a 4-sided polygon whose sides have equal length and adjacent sides form 90-degree angles. It is also a polygon such that rotating about its centre by 90 degrees gives the same polygon. It is not the only polygon with the latter property, however, as a regular octagon also has this property.
So we all know what a square looks like, but can we find all possible squares that can be formed from a set of stars in a night sky? To make the problem easier, we will assume that the night sky is a 2-dimensional plane, and each star is specified by its x and y coordinates.

Input

The input consists of a number of test cases. Each test case starts with the integer n (1 <= n <= 1000) indicating the number of points to follow. Each of the next n lines specify the x and y coordinates (two integers) of each point. You may assume that the points are distinct and the magnitudes of the coordinates are less than 20000. The input is terminated when n = 0.

Output

For each test case, print on a line the number of squares one can form from the given stars.

Sample Input

4
1 0
0 1
1 1
0 0
9
0 0
1 0
2 0
0 2
1 2
2 2
0 1
1 1
2 1
4
-2 5
3 7
0 0
5 2
0

Sample Output

1
6
1

就是看看给出的点能组成几个正方形；
不要四个四个的组合，想也会超时，任意两个组合，然后计算出另外两个点；
再去查询是否存在；结果要除以4的；

#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
bool x[5000][5000];//我才不告诉你其实数据是-2000--2000
int si[1010],sj[1010];
int f(int a,int b)
{
if(x[a+2500][b+2500])
return 1;
return 0;
}
int main()
{
int a,b,i,j,n,sum;
int x1,y1,x2,y2,x3,y3,x4,y4;
while(scanf("%d",&n)&&n)
{
sum=0;
memset(x,0,sizeof(x));
for(i=0; i<n; i++)
{
scanf("%d %d",&a,&b);
si[i]=a;
sj[i]=b;
x[a+2500][b+2500]=1;
}
for(i=1; i<n; i++)
{
x1=si[i];
y1=sj[i];
for(j=0; j<i; j++)
{
x2=si[j];
y2=sj[j];
x3=x1+(y1-y2);//计算剩下两个点
y3= y1-(x1-x2);
x4=x2+(y1-y2);
y4= y2-(x1-x2);
if(f(x3,y3)&&f(x4,y4))
sum++;
x3=x1-(y1-y2);
y3= y1+(x1-x2);
x4=x2-(y1-y2);
y4= y2+(x1-x2);
if(f(x3,y3)&&f(x4,y4))
sum++;
}
}
printf("%d\n",sum/4);//记得除以4
}
return 0;
}

View Code