| Time Limit: 3500MS | Memory Limit: 65536K | |
| Total Submissions: 15489 | Accepted: 5864 |
Description
Input
Output
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
二维平面给定一堆点，求可以组成正方形的个数，点数为1000，因此不能枚举四个点判断，
比较优化的方法是将所有点hash，然后枚举两个点，计算出另外两个点的坐标，然后在hash表里查找，最后结果除以4，因为每一条边被统计了4次。
代码：
/* ***********************************************
Author :_rabbit
Created Time :2014/5/11 8:26:00
File Name :20.cpp
************************************************ */
#pragma comment(linker, "/STACK:102400000,102400000")
#include <stdio.h>
#include <iostream>
#include <algorithm>
#include <sstream>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <string>
#include <time.h>
#include <math.h>
#include <queue>
#include <stack>
#include <set>
#include <map>
using namespace std;
#define INF 0x3f3f3f3f
#define eps 1e-8
#define pi acos(-1.0)
typedef long long ll;
const int maxn=100009;
class HASH{
public:
struct Node{
int next,to;
Node(int _next=0,int _to=0){
next=_next;to=_to;
}
}edge[10010];
int tol,head[maxn+10];
void clear(){
memset(head,-1,sizeof(head));tol=0;
}
void add(int x,int y){
if(find(x,y))return;
int t=(x+maxn)%maxn;
edge[tol]=Node(head[t],y);
head[t]=tol++;
}
int find(int x,int y){
int t=(x+maxn)%maxn;
for(int i=head[t];i!=-1;i=edge[i].next)
if(edge[i].to==y)
return 1;
return 0;
}
}mi;
int x[1010],y[1010];
int main()
{
//freopen("data.in","r",stdin);
//freopen("data.out","w",stdout);
int n;
while(~scanf("%d",&n)&&n){
mi.clear();
for(int i=0;i<n;i++){
scanf("%d%d",&x[i],&y[i]);
mi.add(x[i],y[i]);
// cout<<"hhh "<<endl;
}
ll ans=0;
for(int i=0;i<n;i++)
for(int j=i+1;j<n;j++){
// cout<<"ddd"<<endl;
ll x3,y3,x4,y4;
x3=x[i]+(y[j]-y[i]);y3=y[i]-(x[j]-x[i]);
x4=x[j]+(y[j]-y[i]);y4=y[j]-(x[j]-x[i]);
if(mi.find(x3,y3)&&mi.find(x4,y4))ans++;
x3=x[i]-(y[j]-y[i]);y3=y[i]+(x[j]-x[i]);
x4=x[j]-(y[j]-y[i]);y4=y[j]+(x[j]-x[i]);
if(mi.find(x3,y3)&&mi.find(x4,y4))ans++;
// cout<<"ddd"<<endl;
}
ans/=4;
cout<<ans<<endl;
}
return 0;
}
POJ 2002 点的hash,布布扣,bubuko.com
原文：http://blog.csdn.net/xianxingwuguan1/article/details/25531629