P3388 【模板】割点（割顶）

题目地址

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注意点：

• dfn[x]<=low[nowV].

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#include<cstdio>
#include<iostream>
using namespace std;
const int MAXN=4e4,MAXM=2e5;
struct Edge{
	int from,to,nxt;
}e[MAXM];
int head[MAXN],edgeCnt=1;
void addEdge(int u,int v){
	e[++edgeCnt].from=u;
	e[edgeCnt].to=v;
	e[edgeCnt].nxt=head[u];
	head[u]=edgeCnt;
}
int nowRoot;
int dfn[MAXN],low[MAXN],dfnCnt=0;
bool cut[MAXN];
void tarjan(int x){
	low[x]=dfn[x]=++dfnCnt;
	int flag=0;
	for(int i=head[x];i;i=e[i].nxt){
		int nowV=e[i].to;
		if(!dfn[nowV]){
			tarjan(nowV);
			if(dfn[x]<=low[nowV]){
				flag++;	
				if(x!=nowRoot)cut[x]=1;
			}
			low[x]=min(low[x],low[nowV]);
		}else{
			low[x]=min(low[x],dfn[nowV]);
		}
	}
	if(x==nowRoot&&flag>=2)cut[x]=1;
}
int main(){
	int n,m;
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++){
		int u,v;
		scanf("%d%d",&u,&v);
		addEdge(u,v);
		addEdge(v,u);
	}
	for(int i=1;i<=n;i++){
		if(!dfn[i]){
			nowRoot=i;
			tarjan(i);
		}
	}
	int cutNum=0;
	for(int i=1;i<=n;i++)
		if(cut[i])cutNum++;
	printf("%d
",cutNum);
	for(int i=1;i<=n;i++)
		if(cut[i])printf("%d ",i);
	printf("
");
	return 0;
}