Strongly connected component Tarjan algorithm template

#include<map>
#include<set>
#include<cmath>
#include<stack>
#include<queue>
#include<cstdio>
#include<string>
#include<vector>
#include<cstring>
#include<iomanip>
#include<sstream>
#include<iostream>
#include<algorithm>
#define INF 0x3f3f3f3f
#define ls l,m,rt<<1
#define rs m+1,r,rt<<1|1
//#define ll __int64
//#define int ll
//typedef  long long ll;
typedef unsigned long long ull;
const int MAXN=5e5+10;
const int MOD=1e9+7;
const double eps=1e-6;
using namespace std;
//-------------------------------------------//
vector<int> g[MAXN];
stack<int> s;
int dfn[MAXN],low[MAXN],instack[MAXN],cnt,k;
vector<int> belong[MAXN];
void tarjan(int u)
{
    dfn[u]=low[u]=++cnt;
    s.push(u);
    instack[u]=1;
    for(int i=0;i<g[u].size();++i)
    {
        int v=g[u][i];
        if(!dfn[v])
        {
            tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        else if(instack[v])
        {
            low[u]=min(low[u],dfn[v]);
        }
    }
    if(low[u]==dfn[u])
    {
        int node;
        do
        {
            node=s.top();
            s.pop();
            belong[k].push_back(node);
            instack[node]=0;
        }while(node!=u);
        k++;
    }
}
int main()
{
    //ios::sync_with_stdio(false);
    int n,m;
    cin>>n>>m;
    for(int i=0;i<m;++i)
    {
        int u,v;
        cin>>u>>v;
        g[u].push_back(v);
    }
    tarjan(1);
    for(int i=0;i<k;++i)
    {
        cout<<i+1<<": ";
        for(int j=0;j<belong[i].size();++j)
        cout<<belong[i][j]<<" ";
        cout<<endl;
    }

    return 0;
}

Test Data:

7 11
1 2
2 3
2 5
2 4
3 5
3 7
7 5
5 6
6 7
4 1
4 5