昨天在学校 oj 上过的版本似乎没有判重，看来还是数据弱了。

#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>

using namespace std;

const int N = 2e4 + 10, M = 2e5 + 10;

int h[N], e[M], ne[M], idx, globalTime;

enum COLOR {
    WHITE, GRAY, BLACK
};

COLOR color[N];

int discoverTime[N], back[N],cnt[N];
bool isRoot[N], st[N];
vector<int> ap;

void dfs_ap(int v, int p){
    color[v] = GRAY;
    globalTime ++;
    discoverTime[v] = globalTime;
    back[v] = discoverTime[v];
    for(int i = h[v]; i != -1; i = ne[i]){
        int j = e[i];
        if(color[j] == WHITE){
            cnt[v] ++;
            dfs_ap(j, v);
            if(back[j] >= discoverTime[v] && !isRoot[v] && !st[v]){
                st[v] = true;
                ap.push_back(v);
            }
            back[v] = min(back[v], back[j]);
        }else{
            if(color[j] == GRAY && j != p){
                back[v] = min(back[v], discoverTime[j]);
            }
        }
    }
}

void addArc(int x, int y){
    e[idx] = y;
    ne[idx] = h[x];
    h[x] = idx ++;
}

int main(){
    int n,m;
    cin >> n >> m;
    int x, y;
    memset(h, -1, sizeof h);

    while(m--){
        scanf("%d%d", &x, &y);
        addArc(x, y);
        addArc(y, x);
    }

    for(int i = 1; i <= n; i ++){
        if(color[i] == WHITE){
            isRoot[i] = true;
            dfs_ap(i, -1);
            if(cnt[i] > 1 && !st[i]){
                ap.push_back(i);
                st[i] = true;
            }
        }
    }


    sort(ap.begin(), ap.end());

    int len = ap.size();
    cout << len << endl;
    for(int i = 0; i < len; i ++)cout << ap[i] << " ";

    return 0;
}