[Template] 1: tarjan find cut points

 1 #include<iostream>
 2 #include<cstdio>
 3 using namespace std;
 4 int n,m,idx,cnt,total;
 5 int first[200010],next[200010],to[200010],dfn[100010],low[100010];
 6 bool cut[100010];
 7 void add (int x,int y)
 8 {
 9     to[++cnt]=y;
10     next[cnt]=first[x];
11     First [X] = CNT; // add remember to keep reverse FIG 
12 is  }
 13 is  void Tarjan ( int U, int FA)
 14  {
 15      DFN [U] = Low [U] = IDX ++; // modification timestamps and low values of 
16      int Child = 0 ;
 . 17      for ( int I = First [U]; I = -! . 1 ; I = Next [I])
 18 is      {
 . 19          int NX = to [I];
 20 is          IF (DFN [NX ] == 0 )
 21 is          {
 22 is              Tarjan (NX, FA);
 23 is             low[u]=min (low[u],low[nx]);
24             if (low[nx]>=dfn[u]&&u!=fa)//是根节点单独讨论 
25                 cut[u]=1;
26             if(u==fa)
27                 child++;
28         }
29         else
30         low[u]=min (low[u],dfn[nx]);
31     }
32     if (child>=2&&u==fa)
33         cut[u]=1;
34 }
35 int main()
36 {
37     scanf ("%d%d",&n,&m);
38     for(int i=1;i<=m;i++)
39     {
40         next[i]=-1;
41     }
42     for(int i=1;i<=n;i++)
43     {
44         first[i]=-1;
45     }
46     for (int i=1;i<=m;i++)
47     {
48         int a,b;
49         scanf ("%d%d",&a,&b);
50         add (a,b);
51         add (b,a);
52     }
53     for (int i=1;i<=n;i++)
54         if (dfn[i]==0)
55             tarjan (i,i);
56     for (int i=1;i<=n;i++)
57         if (cut[i]==1)
58             total++;
59     printf ("%d\n",total);
60     for (int i=1;i<=n;i++)
61         if (cut[i]==1)
62             printf ("%d ",i);
63     return 0;
64 }

                                                                                                                  2019-09-08 By the fourteenth day of summer