hdu 2094 

 1 //只需要判断入度为零的点是不是只有1个就可以了
 2 #include<stdio.h>
 3 #include<string.h>
 4 #include<string>
 5 #include<algorithm>
 6 #include<map>
 7 using namespace std;
 8 #define maxn 1005
 9 int indegree[maxn];
10 map<string,int>re;
11 void init()
12 {
13     re.clear();
14     memset(indegree,0,sizeof(indegree));
15 }
16 void topsort(int num)
17 {
18     int count,i;
19     count=0;
20     for(i=1;i<=num;i++)
21         if(indegree[i]==0)
22             count++;
23     if(count==1)
24         printf("Yes\n");
25     else
26         printf("No\n");
27 }
28 int main()
29 {
30     char a[20],b[20];
31     int n,i,j,people;
32     while(scanf("%d",&n)!=EOF&&n)
33     {
34         init();
35         people=1;
36         for(i=1;i<=n;i++)
37         {
38             scanf("%s%s",a,b);
39             if(re[a]==0)
40                 re[a]=people++;
41             if(re[b]==0)
42                 re[b]=people++;
43             indegree[re[b]]++;
44         }
45         topsort(people-1);
46     }
47     return 0;
48 }

 

posted @ 2012-08-10 20:52  M_cag  阅读(166)  评论(0)    收藏  举报