Tarjan求割点 || Luogu P3388 【模板】割点（割顶）

题面：P3388 【模板】割点（割顶） 

题解：无

代码：

#include<cstdio>
#include<iostream>
#include<cstring>
#define max(a,b) ((a)>(b)?(a):(b))
#define min(a,b) ((a)<(b)?(a):(b))
using namespace std;
const int maxn=20000,maxm=1e5;
int N,M,num_edge=0,edge_head[maxn+50],u,v,DFN[maxn+50],LOW[maxn+50];
int ix=0,son,g[maxn+50],ans=0;
struct Edge{
    int to,nx;
}edge[maxm*2+50];
inline void Add_edge(int from,int to){
    edge[++num_edge].nx=edge_head[from];
    edge[num_edge].to=to;
    edge_head[from]=num_edge;
    return;
}
void Tarjan(int x,int fa){
    DFN[x]=LOW[x]=++ix;
    for(int i=edge_head[x];i;i=edge[i].nx){
        int y=edge[i].to;
        if(fa!=y){
            if(DFN[y]==0){
                if(fa==0)son++;
                Tarjan(y,x);
                LOW[x]=min(LOW[x],LOW[y]);
                if(fa!=0&&DFN[x]<=LOW[y]&&g[x]==0){
                    g[x]=1;
                    ans++;
                }
            }
            else LOW[x]=min(LOW[x],DFN[y]);            
        }
    }
    return;
}
int main(){
    scanf("%d%d",&N,&M);
    for(int i=1;i<=M;i++){
        scanf("%d%d",&u,&v);
        Add_edge(u,v);
        Add_edge(v,u);
    }
    for(int i=1;i<=N;i++)
        if(DFN[i]==0){
            son=0;
            Tarjan(i,0);
            if(son>1&&g[i]==0){
                g[i]=1;
                ans++;
            }
        }
    printf("%d
",ans);
    for(int i=1;i<=N;i++)if(g[i])printf("%d ",i);
    return 0;
}

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By:AlenaNuna