割点和割边
\(x's \text{ } son \in T(x)\)
\(Isn't \text{ }x's \text{ }son \in T'(x)\)
\(x \in Cutpoint,y\in T(x) ,y\notin T'(x)\) 。
\(i's\text{ dfs order} \to dfn_i\)
$\min(dfn_{f_y,y\in T(x)}) \to low_x $
\(low_{y,y\in T(x)} \ge dfn_x \to CutPoint\)
\(low_{y,y\in T(x)} \gt dfn_x \to CutEdge\)
\(X=Root ,only \text{ } has \text{ } two \text{ } son\) 。
#include<bits/stdc++.h>
using namespace std;
#define int long long
#define F(i,a,b) for(int i=a;i<=b;i++)
const int Maxn=2e5+5;
int R,Num_CutPoint,dfn[Maxn],cnt,low[Maxn],n,m;
bool CutPoint[Maxn];
vector<int> to[Maxn];
void dfs(int u){
low[u]=dfn[u]=++cnt;
int Son=0;
for(auto &i:to[u]){
if(!dfn[i]){
Son++;dfs(i);low[u]=min(low[u],low[i]);
if(low[i]>=dfn[u]&&u!=R) Num_CutPoint+=(!CutPoint[u]),CutPoint[u]=1;
}else low[u]=min(low[u],dfn[i]);
}
if(u==R&&Son>=2) Num_CutPoint+=(!CutPoint[u]),CutPoint[u]=1;
}
signed main(){
cin>>n>>m;
for(int i=1,u,v;i<=m;i++){
cin>>u>>v;
to[u].push_back(v);
to[v].push_back(u);
}
F(i,1,n) if(!dfn[i]) R=i,dfs(i);
cout<<Num_CutPoint<<endl;
F(i,1,n) if(CutPoint[i]) cout<<i<<" " ;
return 0;
}