哈希技术
#include <stdio.h>
#include <stdlib.h>
#include <memory.h>
#define maxn 1003
typedef struct
{
int x;
int y;
}Node;
Node sq[1003];
typedef struct THashTable{
int x,y;
THashTable* next;
}HashTable;
HashTable* hash[maxn];
void InsertHT(int i)//构建哈希表
{
int key=(sq[i].x)*(sq[i].x)+(sq[i].y)*(sq[i].y);//关键字key
int temH=key%maxn;
if(!hash[temH])
{
HashTable* tem=(HashTable*) malloc(sizeof(HashTable));//易忘点
tem->x=sq[i].x;
tem->y=sq[i].y;
tem->next=0;
hash[temH]=tem;
}
else
{
HashTable* tem=hash[temH];
while(tem->next)
{
tem=tem->next;
}
tem->next=(HashTable*) malloc(sizeof(HashTable));//不要忘了这一步
tem->next->x=sq[i].x;
tem->next->y=sq[i].y;
tem->next->next=0;
}
}
int find(int xx,int yy)
{
int key=xx*xx+yy*yy;//关键字key
int temH=key%maxn;
if(!hash[temH]) return 0;//就没有这个同义词
HashTable* tem=hash[temH];
while(tem)//易错点
{
if(tem->x==xx&&tem->y==yy) return 1;
tem=tem->next;
}
return 0;
}
int main()
{
int n;
while(scanf("%d",&n)&&n!=0)
{
memset(hash,0,sizeof(hash));
int i;
int tot=0;
for(i=0;i<n;i++)
{
scanf("%d %d",&sq[i].x,&sq[i].y);
InsertHT(i);
}
int x3,y3,x4,y4;
for(i=0;i<(n-1);i++)
{
for(int j=i+1;j<n;j++)
{
x3=sq[i].x+(sq[i].y-sq[j].y);
y3=sq[i].y-(sq[i].x-sq[j].x);
x4=sq[j].x+(sq[i].y-sq[j].y);
y4=sq[j].y-(sq[i].x-sq[j].x);
if(find(x3,y3)&&find(x4,y4)) tot++;
x3=sq[i].x-(sq[i].y-sq[j].y);
y3=sq[i].y+(sq[i].x-sq[j].x);
x4=sq[j].x-(sq[i].y-sq[j].y);
y4=sq[j].y+(sq[i].x-sq[j].x);
if(find(x3,y3)&&find(x4,y4)) tot++;
}
}
tot=tot/4;
printf("%d\n",tot);
}
return 0;
}