Strongly Connected Component

#include <bits/stdc++.h>

#define MAX_N 10001
#define ll long long
#define vll vector<ll>
#define all(a) begin(a), end(a)
using namespace std;

ll n, e;
vll adj[MAX_N], radj[MAX_N];
ll rep[MAX_N];
bool vis1[MAX_N], vis2[MAX_N];
vll st;

void dfs1(ll u) {
    vis1[u] = true;
    for(auto& v : adj[u]) {
        if(!vis1[v])
            dfs1(v);
    }
    st.push_back(u);
}

void dfs2(ll u, ll r) {
    rep[u] = r;
    vis2[u] = true;
    for(auto& v : radj[u]) {
        if(!vis2[v])
            dfs2(v, r);
    }
}

vector<vll> solve() {
    for(ll i = 1; i <= n; i++) {
        for(auto& v : adj[i])
            radj[v].push_back(i);
    }

    for(ll i = 1; i <= n; i++) {
        if(!vis1[i])
            dfs1(i);
    }

    while(!st.empty()) {
        ll u = st.back(); st.pop_back();
        if(!vis2[u])
            dfs2(u, u);
    }

    unordered_map<ll, vll> scc;
    for(ll i = 1; i <= n; i++)
        scc[rep[i]].push_back(i);

    map<ll, ll> mp;
    for(auto& [k, v] : scc) {
        sort(all(v));
        mp[v[0]] = k;
    }

    vector<vll> res;

    for(auto& [k, v] : mp) {
        res.push_back(scc[v]);
    }

    return res;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cin >> n >> e;
    while(e--) {
        ll u, v;
        cin>>u>>v;
        adj[u].push_back(v);
    }

    auto res = solve();
    cout<<res.size()<<'\n';
    for(auto& r : res) {
        for(auto& c : r) cout<<c<<' ';cout<<"-1\n";
    }
    return 0;
}