POJ 2002

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;
}