点双连通

#include <cstdio>
#include <vector>
using namespace std;

const int N = 1000+10;
const int M = N*N;

struct Edge {
int u, v;
Edge( int u, int v ):u(u),v(v){}
};

int n, m;
int head
, dest[M], next[M], etot;
int dfn
, low
, bccno
, iscut
, bcc_cnt, idc;
vector<int> bcc
;
vector<Edge> stk;

void adde( int u, int v ) {
etot++;
dest[etot] = v;
next[etot] = head[u];
head[u] = etot;
}
void dfs( int u, int fa ) {
dfn[u] = low[u] = ++idc;
int child = 0;
for( int t=head[u]; t; t=next[t] ) {
int v=dest[t];
if( v==fa ) continue;
stk.push_back( Edge(u,v) );
if( !dfn[v] ) {
dfs(v,u);
low[u] = min( low[u], low[v] );
child++;
if( low[v]>=dfn[u] ) {
iscut[u] = true;
bcc_cnt++;
while(1) {
Edge e=stk.back();
stk.pop_back();
if( !bccno[e.u] ) bccno[e.u]=bcc_cnt,bcc[bcc_cnt].push_back(e.u);
if( !bccno[e.v] ) bccno[e.v]=bcc_cnt,bcc[bcc_cnt].push_back(e.v);
if( e.u==u && e.v==v ) break;
}
}
} else if( dfn[v]<dfn[u] ) {
low[u] = min( low[u], dfn[v] );
}
}
if( u==fa && child<=1 ) iscut[u]=false;
}
int main() {
scanf( "%d%d", &n, &m );
for( int i=1,u,v; i<=m; i++ ) {
scanf( "%d%d", &u, &v );
adde( u, v );
adde( v, u );
}
dfs(1,1);
for( int u=1; u<=n; u++ )
if( iscut[u] ) printf( "%d ", u );
printf( "\n" );
}