POJ 2002 Squares 哈希
题目链接： http://poj.org/problem?id=2002
1 #include <stdio.h> 2 #include <string.h> 3 4 const int prime = 999983; 5 6 struct Hash_table 7 { 8 int x, y; 9 struct Hash_table *next; 10 }*Hash[prime]; 11 12 void Hash_insert(int x, int y) 13 { 14 int key = (x + y) % prime; 15 if(Hash[key] == NULL) 16 { 17 Hash[key] = new Hash_table; 18 Hash[key]->x = x; 19 Hash[key]->y = y; 20 Hash[key]->next = NULL; 21 return; 22 } 23 struct Hash_table *p = Hash[key]; 24 25 //必须注意！下面几行一定是p->next，如果改成： 26 /* 27 while(p != NULL) 28 p = p->next; 29 p = new Hash_table; 30 p->x = x; 31 p->y = y; 32 p->next = NULL; 33 */ 34 //是绝对不行的，因为这里调试了半天了。。。。。。 35 //正解如下： 36 while(p->next != NULL) 37 p = p->next; 38 p->next = new Hash_table; 39 p->next->x = x; 40 p->next->y = y; 41 p->next->next = NULL; 42 } 43 44 bool Hash_search(int x, int y) 45 { 46 int key = (x + y) % prime; 47 struct Hash_table *p = Hash[key]; 48 while(p != NULL) 49 { 50 if(p->x == x && p->y == y) 51 return 1; 52 p = p->next; 53 } 54 return 0; 55 } 56 57 int main() 58 { 59 int n, tx, ty, x[1010], y[1010]; 60 int x3, x4, y3, y4; 61 while(scanf("%d", &n) != EOF && n) 62 { 63 memset(Hash, 0, sizeof(Hash)); 64 for(int i = 0; i < n; i++) 65 { 66 scanf("%d %d", &tx, &ty); 67 x[i] = tx + 20000; 68 y[i] = ty + 20000; 69 Hash_insert(x[i], y[i]); 70 } 71 int ans = 0; 72 for(int i = 0; i < n; i++) 73 { 74 for(int j = 0; j < n; j++) 75 { 76 if(j == i)continue; 77 x3 = x[i]+(y[i]-y[j]); 78 y3 = y[i]-(x[i]-x[j]); 79 x4 = x[j]+(y[i]-y[j]); 80 y4 = y[j]-(x[i]-x[j]); 81 if(Hash_search(x3, y3) && Hash_search(x4, y4)) 82 ans++; 83 } 84 } 85 printf("%d\n", ans/4); 86 } 87 return 0; 88 }
