Tarjan

#define NguyenDangQuan the_author
#define my_heart love_you_to_the_moon_and_back

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;

const int N = 5e4 + 5;
vector<int> adj[N], s;
int n, m, l(0), lt(0);
bool vis[N], on[N];
int low[N], id[N];

void Read(){
    cin >> n >> m;
    while(m--){
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
    }
}

void dfs(int v){
    vis[v] = 1;
    id[v] = low[v] = ++l;
    s.push_back(v);
    on[v] = 1;
    for(auto i : adj[v])
        if(!vis[i]){
            dfs(i);
            low[v] = min(low[v], low[i]);
        }
        else if(on[i])
            low[v] = min(low[v], id[i]);
    if(low[v] == id[v]){
        ++lt;
        int u;
        do{
            u = s.back();
            s.pop_back();
            on[u] = 0;
            cout << u << " ";
        }while(u != v);
        cout << "\n";
    }
}

void Solve(){
    for(int i = 1; i <= n; ++i)
        if(!vis[i])
            dfs(i);
    cout << lt;
}

main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    Read();
    Solve();
}