5524 割点

#include<cstdio>
#include<vector>
using namespace std;
const int N=15005;
vector<int>grap[N];
int n,m,pd,dfn[N],low[N],son,ans;
bool cut[N],mark[N];
void tarjan(int v,int root){
    dfn[v]=low[v]=++pd;
    mark[v]=1;
    for(int i=0;i<grap[v].size();i++){
        int w=grap[v][i];
        if(!dfn[w]){
            tarjan(w,root);
            low[v]=min(low[v],low[w]);
            if(low[w]>=dfn[v]&&v!=root) cut[v]=1;
            else if(v==root) son++;
        }
        else if(mark[w]){
            low[v]=min(low[v],dfn[w]);
        }
    }
}
int main(){
    scanf("%d%d",&n,&m);
    for(int x,y,i=1;i<=m;i++){
        scanf("%d%d",&x,&y);
        grap[x].push_back(y);
        grap[y].push_back(x);
    }
    for(int i=1;i<=n;i++) if(!dfn[i]){
        son=0;
        tarjan(i,i);
        if(son>1) cut[i]=1;
    }
    for(int i=1;i<=n;i++) if(cut[i]) ans++;
    printf("%d",ans);
    return 0;
}