POJ 2002 Squares 哈希

题目链接： http://poj.org/problem?id=2002

 #include <stdio.h>
 #include <string.h>
 
 const int prime = ;
 
 struct Hash_table
 {
     int x, y;
     struct Hash_table *next;
 }*Hash[prime];
 
 void Hash_insert(int x, int y)
 {
     int key = (x + y) % prime;
     if(Hash[key] == NULL)
     {
         Hash[key] = new Hash_table;
         Hash[key]->x = x;
         Hash[key]->y = y;
         Hash[key]->next = NULL;
         return;
     }
     struct Hash_table *p = Hash[key];
 
     //必须注意！下面几行一定是p->next，如果改成：
     /*
     while(p != NULL)
         p = p->next;
     p = new Hash_table;
     p->x = x;
     p->y = y;
     p->next = NULL;
     */
     //是绝对不行的，因为这里调试了半天了。。。。。。
     //正解如下：
     while(p->next != NULL)
         p = p->next;
     p->next = new Hash_table;
     p->next->x = x;
     p->next->y = y;
     p->next->next = NULL;
 }
 
 bool Hash_search(int x, int y)
 {
     int key = (x + y) % prime;
     struct Hash_table *p = Hash[key];
     while(p != NULL)
     {
         if(p->x == x && p->y == y)
             return ;
         p = p->next;
     }
     return ;
 }
 
 int main()
 {
     int n, tx, ty, x[], y[];
     int x3, x4, y3, y4;
     while(scanf("%d", &n) != EOF && n)
     {
         memset(Hash, , sizeof(Hash));
         for(int i = ; i < n; i++)
         {
             scanf("%d %d", &tx, &ty);
             x[i] = tx + ;
             y[i] = ty + ;
             Hash_insert(x[i], y[i]);
         }
         int ans = ;
         for(int i = ; i < n; i++)
         {
             for(int j = ; j < n; j++)
             {
                 if(j == i)continue;
                 x3 = x[i]+(y[i]-y[j]);
                 y3 = y[i]-(x[i]-x[j]);
                 x4 = x[j]+(y[i]-y[j]);
                 y4 = y[j]-(x[i]-x[j]);
                 if(Hash_search(x3, y3) && Hash_search(x4, y4))
                     ans++;
             }
         }
         printf("%d\n", ans/);
     }
     return ;
 }