HDU 1811

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <iostream>
 4 using namespace std;
 5 char s[10005];
 6 int first[30] , k , vis[30];
 7 
 8 struct Edge{
 9     int y , next;
10 }e[100005];
11 
12 void add_edge(int x , int y)
13 {
14     e[k].y = y , e[k].next = first[x];
15     first[x] = k++;
16 }
17 
18 void dfs(int t)
19 {
20     vis[t] = 1;
21     for(int i = first[t] ; i!=-1 ; i=e[i].next){
22         int v = e[i].y;
23         if(!vis[v]) dfs(v);
24     }
25 }
26 int main()
27 {
28   //  freopen("a.in" , "r" , stdin);
29     k = 0;
30     memset(first , -1 , sizeof(first));
31     memset(vis , 0 , sizeof(vis));
32     while(scanf("%s" , s)!=EOF){
33         if(s[0] == ‘0‘){
34             dfs(1);
35             if(vis[(int)(‘m‘-‘a‘)]) puts("Yes.");
36             else puts("No.");
37             k = 0;
38             memset(first , -1 , sizeof(first));
39             memset(vis , 0 , sizeof(vis));
40             continue;
41         };
42         int len = strlen(s);
43         int m = (int)(s[0] - ‘a‘);
44         int n = (int)(s[len-1] - ‘a‘);
45         add_edge(m , n);
46     }
47     return 0;
48 }