1 void tarjan(int u)
 2 {
 3     dfn[u]=low[u]=++dfs_clock;
 4     stack_push(u);
 5     
 6     for (int c=head[u];c;c=nxt[c])
 7     {
 8         int v=to[c];
 9         if (!dfn[v])
10         {
11             tarjan(v);
12             low[u]=min(low[u],low[v]);
13         }
14         else if (!scc[v])
15             low[u]=min(low[u],dfn[v]);
16     }
17     
18     if (low[u]==dfn[u])
19     {
20         scc_cnt++;
21         int cur;
22         for (;;)
23         {
24             scc_size[scc_cnt]++;
25             cur=stack_pop();
26             scc[cur]=scc_cnt;
27             if (cur==u)
28                 break;
29         }
30     }
31 }