代码：

#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5e5 + 5;
vector<int> ans[MAXN];
int dfn[MAXN], low[MAXN], visited[MAXN]; 
int head[MAXN], ver[MAXN * 2], Next[MAXN * 2];
int num = 0;
int root, dcc, tot;
bool bridge[MAXN];
void add(int x, int y) {
	ver[++tot] = y;
	Next[tot] = head[x];
    head[x] = tot;
}
void tarjan(int i, int in_edge) {
	dfn[i] = low[i] = ++num;
	for(int j = head[i]; j ; j = Next[j]) {
		int v = ver[j];
		if(!dfn[v]) {
			tarjan(v, j);
			low[i] = min(low[i], low[v]);
			if(low[v] > dfn[i]) {
				bridge[i] = bridge[i ^ 1] = true;
			}
		}else if(i != (in_edge ^ 1)) low[i] = min(low[i], dfn[v]);
	}
}
void dfs(int i) {
	visited[i] = dcc;
	if(i) ans[dcc].push_back(i);
	for(int j = head[i]; j ; j = Next[j]) {
		int v = ver[j];
		if(visited[v] || bridge[j]) continue;
		dfs(v);
	}
}
int main() {
	int n, e;
	cin >> n >> e;
	for(int i = 1; i <= e; i++) {
		int u, v;
		cin >> u >> v;
		if(u == v) continue;
		add(u, v);
		add(v, u);
	}
	for(int i = 1; i <= n; i++) {
		if(!dfn[i]) {
			root = i;
			tarjan(i, 0);
		}
	}
	for(int i = 1; i <= n; i++) {
		if(!visited[i]) {
			++dcc;
			dfs(i);
		}
	}
	cout << dcc << endl;
	for(int i = 1; i <= dcc; i++) {
		cout << ans[i].size() << " ";
		for(int j = 0; j < ans[i].size(); j++) {
			cout << ans[i][j] << " ";
		}
		cout << endl;
	}
	return 0;
}

测试结果