Tarjan algorithm || Find strongly connected component

#include <bits/stdc++.h>
#define int long long
using namespace std;
const int N = 3*1e5+5;
const int inf = 10000000000005;

int n,m,cnt=0,lt=0;
vector<int> a[N];
vector<int> num,low,res[N];
stack<int> st;

void dfs(int u)
{
    num[u]=low[u]=++cnt;
    st.push(u);
    for(int v : a[u])
    {
        if (num[v]) low[u] = min(low[u], num[v]);
        else
        {
            dfs(v);
            low[u] = min(low[u],low[v]);
        }
    }
    if (num[u]==low[u])
    {
        ++lt;
        int v;
        do
        {
            v = st.top();
            st.pop();
            res[lt].push_back(v);
            low[v] = num[v] = inf;
        } while (v != u);
    }
}

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie();cout.tie(0);
    cin >> n >> m;

    num.resize(n+1,0);
    low.resize(n+1,0);

    while (m--)
    {
        int u,v;
        cin >> u >> v;
        a[u].push_back(v);
    }
    for(int i=1; i<=n; ++i)
    {
        if (!num[i]) dfs(i);
    }
    cout << lt << endl;
    for(int i=1; i<=lt; ++i)
    {
        cout << res[i].size() << endl;
        for(int v : res[i]) cout << v << " ";
        cout << endl;
    }
    return 0;

}