POJ 2230 Watchcow

 1 #include <cstdio>
 2 #include <cstring>
 3 using namespace std;
 4 const int maxn = 10010;
 5 struct arc {
 6     int to,next;
 7     arc(int x = 0,int y = -1) {
 8         to = x;
 9         next = y;
10     }
11 } e[500000];
12 int head[maxn],tot,n,m;
13 bool vis[500000];
14 void add(int u,int v) {
15     e[tot] = arc(v,head[u]);
16     head[u] = tot++;
17 }
18 void dfs(int u) {
19     for(int &i = head[u]; ~i; i = e[i].next) {
20         if(vis[i]) continue;
21         vis[i] = true;
22         dfs(e[i].to);
23     }
24     printf("%d\n",u);
25 }
26 int main() {
27     int u,v;
28     while(~scanf("%d%d",&n,&m)) {
29         memset(head,-1,sizeof head);
30         memset(vis,false,sizeof vis);
31         for(int i = tot = 0; i < m; ++i) {
32             scanf("%d%d",&u,&v);
33             add(u,v);
34             add(v,u);
35         }
36         dfs(1);
37     }
38     return 0;
39 }