POJ 2002 Squares（哈希表）
给n个点，找有多少个正方形。忘记初始化了。。。纳闷哈希为毛线一直TLE呢，明显不科学啊。。。哈希跑的还是比较快的，乱搞随便一个哈希函数，跑了500+。
还有 知道对角线两点坐标，求另外两点。。。懒的手推，百度知道上有。。。
1 #include <iostream> 2 #include <cstdio> 3 #include <cstdlib> 4 #include <cstring> 5 #include <cmath> 6 #include <string> 7 using namespace std; 8 #define MOD 177777 9 #define MAXN 1000000 10 struct node 11 { 12 int data; 13 struct node *next; 14 }*head[MOD],hash[MAXN]; 15 int x[1001],y[1001]; 16 int judge(int xx,int yy) 17 { 18 node *p; 19 int key = xx*1000 + yy; 20 key = key%MOD; 21 if(key < 0) 22 key += MOD; 23 for(p = head[key];p != NULL;p = p->next) 24 { 25 if(x[p->data] == xx&&y[p->data] == yy) 26 return p->data; 27 } 28 return 0; 29 } 30 int main() 31 { 32 int n,i,j,num,ans,key; 33 int x3,y3,x4,y4,flag1,flag2; 34 while(scanf("%d",&n)!=EOF) 35 { 36 if(n == 0)break; 37 for(i = 0;i < MOD;i ++) 38 head[i] = NULL; 39 num = 0; 40 ans = 0; 41 for(i = 1;i <= n;i ++) 42 { 43 scanf("%d%d",&x[i],&y[i]); 44 key = x[i]*1000 + y[i]; 45 node *p; 46 p = &hash[num++]; 47 p -> data = i; 48 key = key%MOD; 49 if(key < 0) 50 key += MOD; 51 p -> next = head[key]; 52 head[key] = p; 53 } 54 for(i = 1;i <= n-1;i ++) 55 { 56 for(j = i+1;j <= n;j ++) 57 { 58 x3 = x[i]+x[j]+y[j]-y[i]; 59 if(x3%2 != 0) continue; 60 x3 = x3/2; 61 y3 = y[i]+y[j]-x[j]+x[i]; 62 if(y3%2 != 0) continue; 63 y3 = y3/2; 64 x4 = x[i]+x[j]+y[i]-y[j]; 65 if(x4%2 != 0) continue; 66 x4 = x4/2; 67 y4 = y[i]+y[j]-x[i]+x[j]; 68 if(y4%2 != 0) continue; 69 y4 = y4/2; 70 flag1 = judge(x3,y3); 71 flag2 = judge(x4,y4); 72 if(flag1&&flag2) ans ++; 73 } 74 } 75 printf("%d\n",ans/2); 76 } 77 return 0; 78 }
