Biconexitate

// https://www.pbinfo.ro/probleme/1572/componentebiconexe
#include <fstream>
#include <algorithm>
#include <vector>
#include <array>
using namespace std;
ifstream cin("componentebiconexe.in");
ofstream cout("componentebiconexe.out");
#define RADACINA 1
const int mxN = 1e5;
vector<int> adj[mxN+10],order,compBi[mxN+10], pA; // pA -> puncte de articulatie
vector<array<int,2>> mC; // mC -> muchii critice
int depth[mxN+10], minD[mxN+10]; // minD -> nivel minim accesibil
int visited[mxN+10], nrCompBi;
void DFS(int node, int parent)
{
    order.push_back(node); // order -> ordinea in care sunt parcurse nodurile in DFS
    visited[node] = true;
    depth[node] = depth[parent] + 1;
    minD[node] = depth[node];
    int cntVis = 0;
    bool isCrit = false; // daca este punct de articulatie / nod critic
    for(auto it : adj[node])
    {
        if(it == parent) continue;
        if(visited[it])
            minD[node] = min(minD[node], depth[it]);
        else
        {
            cntVis++;
            DFS(it,node);
            minD[node] = min(minD[node],minD[it]);
            if(depth[node] <= minD[it]) isCrit = true;
            if(depth[node] < minD[it])
                mC.push_back({node,it});
            if(depth [node] <= minD[it]) // componenta biconexa
            {
                nrCompBi++;
                while(order.back() != it)
                    compBi[nrCompBi].push_back(order.back()), order.pop_back();
                // fac parte din componenta si (node) si (it) care inca nu sunt adaugate.
                compBi[nrCompBi].push_back(node);
                compBi[nrCompBi].push_back(it);
                order.pop_back(); // era it acum.
            }

        }
    }
    if(node == RADACINA && cntVis < 2)
        isCrit = false;
    if(isCrit)
        pA.push_back(node);
}
int main()
{
    int cerinta;
    cin >> cerinta;
    int n , m ;
    cin >> n >> m;
    for(int i = 1;i<=m;i++)
    {
        int a, b;
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    DFS(1,0);
    if(cerinta == 1) // sa se afiseze componentele biconexe
    {
        cout << nrCompBi << '\n';
        for(int i = 1;i<=nrCompBi;i++)
        {
            cout << compBi[i].size() << ' '; // nr de elem din componenta
            for(auto it : compBi[i]) // afisam elementele din componenta
                cout << it << ' ';
            cout << '\n';
        }
    }
    if(cerinta == 2) // sa se afiseze punctele  de articulatie  (punctele critice)
    {
        cout << pA.size() << '\n';
        for(auto it : pA)
            cout << it << ' ';
        cout << '\n';
    }
    if(cerinta == 3) // sa se afiseze puntile (muchiile) critice
    {
        cout << mC.size() << '\n';
        for(auto it : mC)
            cout << it[0] << ' ' << it[1] << '\n';
    }
    return 0;
}