hdu1325 Is It A Tree? 基础并查集 

 1 #include <stdio.h>  
 2 #include <string.h>  
 3 
 4 int f[1001], g[1001];
 5 
 6 int find(int x)        //并查集的查找，找到共同的父亲  
 7 {
 8     if (f[x] != x)
 9         f[x] = find(f[x]);
10     return f[x];
11 }
12 
13 int main()
14 {
15     int a, b, tt = 1;
16     while (scanf("%d%d", &a, &b) != EOF)
17     {
18         int i, flag = 0, t = 0;
19         if (a<0 && b<0)              
20             break;
21         for (i = 0; i <= 1000; i++)
22             f[i] = i;
23 
24         //合并
25         if (find(a) == find(b))
26             flag = 1;
27         else
28             f[find(b)] = find(a);
29 
30         while (scanf("%d%d", &a, &b))
31         {
32             if (a == 0 && b == 0)
33                 break;
34             int aa, bb;
35             aa = find(a);
36             bb = find(b);
37             //合并
38             if (aa == bb || bb != b)   //成环就不是树，后面的是检查是否有两个父节点  
39                 flag = 1;
40             else
41                 f[bb] = aa;
42         }
43 
44         memset(g, 0, sizeof(g));
45         for (i = 1; i <= 1000; i++)    //保证只有一个根，不然就是森林了  
46         if (f[i] != i)
47             g[find(i)]++;
48         for (i = 1; i <= 1000; i++)    //检查是否只有一个头结点就是了  
49         if (g[i]>0)
50             t++;
51         if (t>1)
52             flag = 1;
53         if (flag == 1)
54             printf("Case %d is not a tree.\n", tt++);
55         else
56             printf("Case %d is a tree.\n", tt++);
57     }
58     return 0;
59 }

 

posted @ 2017-07-20 19:11  ouyang_wsgwz  阅读(141)  评论(0)    收藏  举报